The Effect of Climatic Variations on Agricultural Risk

Working Paper

THE EFFECT OF c m n c VARIATIONS ON

AGRICULTURAL

RISK

M.L. Parry

T.R.

Carter

August 1984 WP-84-69

International Institute for Applied Systems Analysis

A-2361 Laxenburg, Austria

NOT FOR QUOTATION WITHOUT PERMlSSlON OF THE AUTHOR

THE EFFECT OF CLIMATIC

VAFUATIONS ON

AGRICLKTURAL RISK

M.L.

P a r r y

T.R.

Carter

August

1984 WP-84-69

Working Papers a r e interim reports on work of the International Institute for Applied Systems Analysis and have received only limited review. Views o r opinions expressed herein do not necessarily r e p r e s e n t those of t h e l n s t i t u t e or of its National Member Organizations.

INTERNATIONAL INSTITUTE FOR APPLIED SYSTEMS ANALYSIS 2361 Laxenburg, Austria

Over t h e p a s t decade t h e international scientific community and even t h e popular media have been paying increasing attention to long-range c l i m a t e change--the e x t e n t and timing of global warming, shifts in precipitation p a t t e r n s , ecological, economic, and even geo-political effects.

Considerable research attention should obviously be addressed to t h e pros- p e c t s for a n d implications of seminal climate change; such a development could have historic consequences. But t h e global scale a n d t h e long-term n a t u r e of t h e challenge, together with t h e uncertainties still to be resolved, t e n d to make t h e COz/climate issue, as i t is usually presented, a residual claimant for t h e t i m e a n d a t t e n t i o n of national a n d international policy communities. This w o r k n g paper, 7he Effect of Climatic lh'ariations o n AgricILltIL~al

Risk,

approaches t h e problem of c l i m a t e change from a different perspective in t e r m s of both spatial and temporal scales. It addresses "present day impacts from short-term climate variability".

And i t examines, as a case in point, t h e shifts of climate-related risk level a n d agri- c u l t u r a l growth potential for a single crop (oats) in a single locality ( s o u t h e r n Scot- land).

But, however interesting t h i s may be a s a n exercise in analyzing t h e climate- risk issue u n d e r a particular s e t of conditions in a particular a r e a , t h e authors have a l a r g e r objective in mind: t h e y wish t o use t h e i r investigation of change of risk as a building block for assessing the consequences for agriculture of long-term (C02- induced) climate change. Such an approach, I believe, will provide useful guidance for those contemporary officials for whom a relatively remote, world-wide shift on t e m p e r a t u r e a n d precipitation is too emphemeral to appear on already-crowded policy agendas.

Professor Martin P a r r y a n d his associates a t IIASA a r e investigating t h e i m p a c t s of s h o r t - t e r m climatic variations and t h e likely long-term 'effects of COz- i n d u c e d climatic changes on food output a t t h e sensitive margins of production.

This work is p a r t of a two-year effort a n d is expected t o be completed. by December, 1985.

Dr. Chester

L.

Cooper Special Advisor t o the Director Acting Head of t h e Environmental Program

The t h e s i s of this paper is t h a t impacts from climatic change can be evaluated effectively as changes in t h e frequency of short-term, anomalous climatic events.

These c a n t h e n be expressed a s changes in the level of risk of impact from climatic extremes. To evaluate this approach, t h e risk of crop failure resulting from low lev- els of a c c u m u l a t e d t e m p e r a t u r e is assessed for oats farming in southern Scotland.

Annual accumulated t e m p e r a t u r e s a r e calculated for t h e 323-year long tempera- t u r e record compiled by Manley for Central England. These a r e bridged across t o southern Scotland and, by calculating mean levels of risk for different elevations, an average "risk surface" is constructed. I-in-10 and 1-in-50 frequencies of crop failure a r e assumed to delineate a high-risk zone, which is mapped for the 323-year period by constructing isopleths of these risk levels. By re-dravling the risk iso- pleths for warm a n d cool 50-year periods, t h e geographical shift of t h e high-risk zone is delineated. The conclusion is t h a t relatively r e c e n t a n d apparently minor climatic variations in the United Kingdom have in fact induced substantial spatial c b m g e s in levels of agricultural risk. h advantage of expressing climatic change as a change in agricultural risk, is t h a t support programs for agriculture can be re-tuned t o accommodate acceptable frequencies of impact by adjusting support levels t o m a t c h new risk levels.

CONTENTS

1. Introduction

2. Long-Term Variations in Growth Potential 2.1. Selection ,of t h e P a r a m e t e r

2.2. Central England Accumulated Temperatures, 1659-1981 2.3. The Chronology of Accumulated Warmth

2.4. Derivation of Proxy Accumulated Temperatures for Southern Scotland 2.4.1.Bridging from Central England to Edinburgh

2.4.2.Bridging from E b n b u r g h to Southern Scotland 3. The Frequency of Crop Failure

3.1. Method

3.2. Predicting t h e Location of Crop Failure 4. A Risk Surface of Crop Failure

5. Delimiting High-Risk Areas

6. Changes in t h e Frequency of Crop Failure 7. Conclusions

References

-

^vii

-

THE

m C T

OF CLIMATIC VARIATIONS ON AGRICULTURAL RISK

M.L.

P a r r y a n d T.R. C a r t e r

1. Introduction

In t h e field of climate impact a s s e s s m e n t t h e r e h a s been a tendency t o distin- guish between t h e role of short-term climatic variability a n d t h e role of long-term climatic change. One affects t h e range a n d frequency of shocks t h a t society absorbs or to which i t adjusts. The o t h e r a l t e r s t h e r e s o u r c e base, for example t h e agro-climatic resources t h a t can affect farming options a n d t h e patterns of com- parative advantage, which themselves help t o d e t e r m i n e why some crops a r e grown in one place and different crops in another. Follow-ing this line of thought, some studies have a t t e n d e d specifically t o those shifts of cropping zones t h a t might o c c u r a s a result of long-term changes in m e a n c l i m a t e (Williams and Oakes, 1978;

Newman, 1980).

Yet this distinction between s h o r t - t e r m a n d long-term reflects more statistical convenience t h a n an understanding of h u m a n behavior. Few societies or individu- als look far ahead or behind. Farmers, for example, m a y plan over one or two y e a r s but rarely m o r e t h a n five. Any future i m p a c t from long-term changes in m e a n cli- m a t e c a n t h u s be seen a s being embedded in p r e s e n t - d a y impacts from short-term climatic variability; and i t is likely t h a t t h e s e s h o r t - t e r m impacts will remain t h e medium through which a n y long-term change i s felt. The thesis of this paper is, therefore, t h a t impacts from climatic change should be expressed as changes in r i s k of i m p a c t from t h e s h o r t - t e r m anomalous event. One advantage of considering possible impacts from climatic changes in t h i s form is t h a t t h e y c a n be expressed in a language understood by t h e policy-maker. Present-day frequencies of climatic events c a n be u s e d a s a base upon which t o impose effects, such as C02-induced warming, t o obtain modified frequencies reflecting t h e possible impacts of costly,

e x t r e m e events ( s u c h as droughts, floods, cold spells, etc.). Government programs can t h e n be devised t o accommodate specified tolerable levels of risk, by adjusting activities as necessary t o match t h e change in risk.

In this paper we explore t h e e x t e n t t o which levels or climate-related risk have varied in t h e past, as indicated by t h e instrumental record. Our choice of d a t a and study a r e a was governed by two requirements: firstly, for a long instrumental record (to d e t e c t impacts from s h o r t - t e r m changes in p a t t e r n s or climatic variabil- ity); secondly, t o examine a region where climatic risk is high, and where changes in climatic risk would have a readily detectable effect on t h e economic system.

Subsequently, with a deeper u n d e r s t a n h n g of t h e issue, an investigation of this kind can be extended to regions where climatic risk is less pronounced b u t nonetheless still important.

.

The longest i n s t r u m e n t a l record available is t h a t for t e m p e r a t u r e in Central England compiled by Manley (1953, 1974). This is representative of inland locations in t h e English Midlands a t about 150 feet (46m) above s e a level. At this elevation, however, levels of climate-related r i s k for agriculture a r e n o t high. For a con- venient laboratory, we t h u s n e e d t o look a t upland a r e a s with higher levels of risk.

An appropriate one is the Southern Uplands of Scotland which previous work h a s indicated a s being characterized by highly marginal forms of arable agriculture ( P a r r y , 1975). We shall focus specifically on t h e cultivation of oats which, a t eleva- tions qf a b o u t 340 m in southern Scotland, is n e a r i t s physiological limit.

Howevrr, t h e i n s t r u m e n t a l record for this region extends back only t o 1856.

Only a t Ldinburgh is it e x t a n t for t h e 1Bth c e n t u r y (from 1764). For t h e period before 1764 we m u s t look to t h e data for Central England available from 1659. By bridging between the data s e t s for Central England and Edinburgh, a n d between those for Edinburgh and our upland region, it is possible t o derive a 323-year r u n of t e m p e r a t u r e d a t a for southern Scotland. We shall analyze these data for long-term changes in climatic risk, first in Central England a n d subsequently in s o u t h e r n Scotland, a n d assess t h e i m p a c t of t h e s e changes on marginal agriculture in t h e upland region.

2. Long-Tern Variations ID

Growth

Potential 2.1. Selection of the Parameter

In m a r i t i m e upland a r e a s relatively small increases in altitude generally r e s u l t in m a r k e d foreshortening of t h e growing season a n d a g r e a t reduction i n t h e inten- sity of accumulated warmth (Manley, 1945). Moreover, t h e variability of accumu- lated warmth relative t o t h e m e a n increases with altitude, a n d f u r t h e r contributes t o t h e rapid altitudinal fall in potential for crop grovrfh (Manley, 1951).

For oats, which is m o r e t o l e r a n t of high rainfall, frequent soil waterlogging a n d g r e a t e r soil acidity t h a n a r e wheat and barley, t h e intensity of growing season t e m - p e r a t u r e s i s t h e single m o s t limiting climatic factor. The most effective m e a s u r e of this is one of accumulated t e m p e r a t u r e (or the n u m b e r of groxving degree-days, GDD). Growing degree-days a r e calculated as t h e excess of mean monthly tempera- t u r e ( & ) over t h e base t e m p e r a t u r e (t,), multiplied by t h e n u m b e r of days in t h e m o n t h ( m i ) and cumulated over one year t o give a n annual total (A):

12

A = mi(&-t,) for

fi

r

t b

i =I

We have used a base of 4 . 4 " ~ , one established from phenological studtes a s being appropriate for oats in n o r t h e r n Europe (Nuttonson, 1955), t o calculate annual accumulated t e m p e r a t u r e s for Central England from 1659 t o 1981.

2.2. Central England Accumulated Temperatures, 1659-1 98 1

Central England t e m p e r a t u r e s were assembled by Manley from several discon- tinuous series into a table of monthly means. This was derived from t h e average of data recorded in Oxford a n d a t a n u m b e r of stations in Lancashire from 1815. Data for the period from 1771 t o 1815 were obtained by averaging t h e departures for each month a t a n u m b e r of inland stations whose records a r e sufficiently long t o be

"bridged" into the l a t e r r u n of data. For t h e period before 1771 d a t a were bridged into the record from a variety of s c a t t e r e d observation points.

From these monthly d a t a accumulated t e m p e r a t u r e s in month-degrees were calculated by Manley (1951) for the period 1751-1949 for sites a t a height of 183 m in t h e English Pennines. However, using t h e full r u n of d a t a , we have calculated growing degree-days a t 46 m ( t h e height represented by t h e Central England tem- perature data) for a 323-year period (Figure 1).

2.3. The Chronology of Accumulated Warmth

The history of t h e s e a c c u m u l a t e d t e m p e r a t u r e s is, in one s e n s e , a barometer of t h e buoyancy of t h e local farming economy, particularly i n t h e cold, marginal uplands of n o r t h e r n Europe agriculture is so constrained by a growing season which is both s h o r t and lacking in intensity. The m o s t i m p o r t a n t events in this chronology (bearing in mind t h a t i t represents lowland conditions) were probably the cooler-than-average y e a r s , particularly those with less t h a n 90 p e r c e n t of m e a n accumulated warmth (about 1660 GDD). We can classify t h e s e e x t r e m e occurrences into: (1) those t h a t a r e single, isolated extremes (e.g. 1740, 1782, 1860, 1879, 1922);

(2) those t h a t r e p r e s e n t clustered, successive events of two, t h r e e or even more extremes in a row (e.g. 1673-75, 1686-98, 1838-40, 1887-88, 1891-92); and (3) those t h a t represent periods c h a r a c t e r i z e d by a high frequency of s c a t t e r e d , not succes- sive negative e x t r e m e s (e.g. 1812-1 7, 1679-92). Though n o t necessarily mutually exclusive, these could have recognizably h f f e r e n t effects: t h e isolated e v e n t hav- ing a sudden but short-lived impact, while successive e x t r e m e s bring a b o u t increas- ingly greater economic hardship.

For example 1740 saw a spectacularly poor h a r v e s t in Scotland, yet. food shor- tages were made good t h e following s u m m e r (Parry, 1978). Similarly, t h e cool sum- m e r of 1782 delayed t h e upland oats harvest until December. In Aberdeenshire farmers had to shake t h e snow- off t h e crop before cutting (Pearson, 1973). Yet t h e r e was little lasting hardship.

The limited i m p a c t of such isolated events can be c o n t r a s t e d with t h e effects of a r u n of extreme y e a r s which, by forcing f a r m e r s to consume t h e i r seed stocks or spend their cash reserves, could seriously prejudice t h e i r harvests in subsequent years. In this respect, t h e effect of the so-called "Seven Ill Years" of t h e 1690s on the rural population in n o r t h e r n Europe was catastrophic. In Finland a t least a quarter, a n d possibly a t h i r d , of the population &ed in t h e Great Famine of 1696-97 largely as a result of epidemic diseases spreading through a n ill-fed a n d weak popu- lation (Jutikkala, 1955).

Finally, we can d e t e c t t h e cumulative, erosive effect of t h e periods c h a r a c t e r - ized by frequent, b u t s c a t t e r e d extremes. In t h e s e instances, t h e process of recovery was halted a n d reversed by a series of r e c u r r e n t shocks t h a t , over several years, t h e farm economy h a d insufficient s t a m i n a or resilience t o absorb. In the U.K. the scattered e x t r e m e s over 1879-92 slowly brought m o r e and m o r e f a r m e r s to a s t a t e of bankruptcy, particularly because grain prices, held back by cheap imports since t h e repeal of tariffs on Korth American grain, failed t o respond to depressed yields (Perry, 1974; Royal Commission, 1683).

S u c h h i s t o r i c a l , ideographic descriptions of t h e e f f e c t s of single, s u c c e s s i v e , and c l u s t e r e d e x t r e m e s a r e , however, n o t a sufficient basis for g e n e r a l i z a t i o n s con- cerning t h e i m p a c t on a g r i c u l t u r e of c l i m a t i c variability a n d of c h a n g e s in t h a t variability. S u c h a basis can only be provided by s t u d y of specific r e s p o n s e s in p a r - t i c u l a r f a r m i n g s y s t e m s . We shall focus specifically on t h e probability of c r o p failure b e c a u s e we believe t h a t t h i s is a m o s t effective m e a s u r e of i m p a c t f r o m c l i m a t i c v a r i a t i o n s . There a r e two r e a s o n s for t h i s . Firstly, m a r g i n a l f a r m e r s , by definition, o p e r a t e n e a r t h e l i m i t s of profitability a n d a r e m o r e c o n c e r n e d with s u r - vival (i-e. probability of t h e i r avoiding failure) t h a n with a c c u m u l a t i n g wealth (i.e.

t h e i r i n c r e m e n t above a m i n i m u m average condition). Secondly, t h e n o n - m a r g i n a l , profit-maximizing f a r m e r knows well t h a t n e t r e t u r n s a r e n o t simply a f u n c t i o n of average yield, b u t also of t h e balance s t r u c k between gambling on "good" y e a r s a n d insuring a g a i n s t "bad" ones (Edwards, 1978).

We shall f o c u s on t h o s e c h a n g e s in probability of c r o p failure t h a t can o c c u r a s a r e s u l t of c h a n g e s of climate. To do t h i s , however, r e q u i r e s a long r u n of d a t a . These a r e o b t a i n e d by bridging a c r o s s t o o u r u p l a n d s t u d y region f r o m t h e C e n t r a l England t e m p e r a t u r e record.

2.4. Derivation of Proxy Accumulated T e m p e r a t u r e s f o r S o u t h e r n S c o t l a n d

A 323-year proxy r e c o r d of a c c u m u l a t e d t e m p e r a t u r e s for s o u t h e r n Scotlalld was c o n s t r u c t e d by bridging from Central England t o Edinburgh, a n d f r o m Edin- burgh t o a network of 27 s t a t i o n s covering t h e s t u d y a r e a .

2.4.1. Bridging

from

Central England t o Edinburgh

Data for t h e period of overlap between t h e two r e c o r d s (1764-1896) w e r e analyzed t o establish l i n e a r regression e q u a t i o n s , f o r e a c h m o n t h , of Edinburgh t e m p e r a t u r e s on Central England t e m p e r a t u r e s . Correlation coefficients w e r e also recorded, a n d all indicate a close relationship between t h e two s e t s of m o n t h l y t e m - p e r a t u r e s (significant a t t h e 99 p e r c e n t level). A plausible m e a n s of e x t r a p o l a t i n g t h e Edinburgh r e c o r d is, t h e r e f o r e , t o u s e t h e r e g r e s s i o n coefficients a s p r e d i c t o r s of t e m p e r a t u r e s a t Edinburgh for t h e full period, 1659-1931.

2.4.2. Bridging from Edinburgh to Sou t h e r n S c o t l a n d

Twelve regression equations relating m e a n m o n t h l y t e m p e r a t u r e s t o elevation were c a l c u l a t e d , o n e for each m o n t h , f r o m t h e 40-year r e c o r d (1856-1895) for t h e 27 s t a t i o n s (excluding Edinburgh) in s o u t h e r n Scotland. These e q u a t i o n s w e r e u s e d t o e s t i m a t e m o n t h l y m e a n s (1856-95) for a s i t e r e p r e s e n t a t i v e of t h e whole region at t h e s a m e a l t i t u d e a s t h e Edinburgh s t a t i o n (76 m). The differences between t h e s e e s t i m a t e s a n d t h e a c t u a l monthly m e a n s for Edinburgh, w e r e t h e n u s e d a s c o r r e c t i o n f a c t o r s t o a d j u s t t h e proxy Edinburgh d a t a t o obtain longer-term t e m - p e r a t u r e s for t h e study a r e a . We can t h u s derive a 323-year s e t of a c c u m u l a t e d t e m p e r a t u r e s for s o u t h e r n Scotland, within which t o e x a m i n e t h e f r e q u e n c y of c r o p failure.

3. T h e Frequency of Crop Failure 3.1. Method

For m a n y c r o p s t h e point of "failure" i s a n a r b i t r a r y one b e c a u s e , however small t h e r e t u r n of grain, t h e residue m a t e r i a l (straw, e t c . ) is often valuable as fodder. There is a point, however, where t h ~ g r a i n yield falls so far s h o r t of t h e e x p e c t e d yield o r t h e yield required t o cover c o s t s of i n p u t s s u c h a s s e e d , l a b o r a n d fertilizers t h a t , in economic t e r m s , t h e y e a r ' s v e n t u r e m a y be considered a failure.

Clearly c r o p failure can t h u s be defined in m a n y different ways, e a c h a p p r o p r i a t e

for different f a r m i n g s y s t e m s a n d c r o p types.

Our definitions a n d d a t a for c r o p failure ref.er t o Red and Blaislie v a r i e t i e s of oats which were c o m m o n l y grown in t h e s t u d y region in t h e n i n e t e e n t h c e n t u r y . By e x a m i n i n g diaries and f a r m journals for t h a t period we can identify t h e y e a r s of crop failure and, by referring t o t h e meteorological r e c o r d , t h e w e a t h e r of t h o s e dismal s u m m e r s . Empirically, i t h a d been concluded from e a r l i e r work t h a t w h e r e a c c u m u l a t e d t e m p e r a t u r e s failed t o exceed 970 degree-days o a t s h a r v e s t s were e x t r e m e l y delayed a n d r e d u c e d ( P a r r y , 1978).

Knowing t h e l a p s e r a t e of t e m p e r a t u r e with elevation in t h e region (0.6B°C/100 m, P a r r y . 1976), i t is possible t o c a l c u l a t e , for e a c h y e a r , t h e h e i g h t a t which t h e m i n i m u m a c c u m u l a t e d t e m p e r a t u r e i s achieved. Above t h i s h e i g h t , which shifts upwards a n d downwards substantially f r o m y e a r t o y e a r according t o variations in a c c u m u l a t e d w a r m t h , t h e o a t s c r o p would h a v e been long delayed (Figure 2). We t h u s h a v e a p i c t u r e , for t h e period 1659 t o 1981, of t h e year-to-year s h i f t s in t h e h y p o t h e t i c a l u p p e r limit of t h e o a t s c r o p c a u s e d by a n n u a l v a r i a t i o n s in t e m p e r a - t u r e . In t h i s way, c l i m a t i c v a r i a t i o n s c a n be e x p r e s s e d a s t h e spatial variation of a boundary, which s h i f t s a c r o s s a n e c o n o m i c surface: t h u s a f a r m e r who in one y e a r lies on t h e "right" side of t h e boundary and, c e t e r i s pa. :;us, h a s an o a t s c r o p t o h a r v e s t , m a y in a n o t h e r l i e on t h e "wrong" side a n d r e c o u p ver; little. I t is b u t a simple s t e p t o e x p r e s s t h a t f a r m e r ' s position in t e r m s of risk of c r o p failure d u e t o i n a d e q u a t e a c c u m u l a t e d w a r m t h a n d , f u r t h e r m o r e , t o e x p r e s s c l i m a t i c c h a n g e s a s c h a n g e s in t h a t level of risk. Before doing so, however, i t is useful t o explore t h e value of Figure 2 a s a predictive tool i n historical r e s e a r c h and. in s o doing, t o pro- vide s o m e verification of t h e model.

3.2. Predicting the Location of Crop Failure

Following t h e t r i p a r t i t e classification i n t r o d u c e d e a r l i e r , we c a n p r e d i c t t h e locations a t which c r o p failure o c c u r r e d e i t h e r i n indtvidual e x t r e m e y e a r s o r in successive e x t r e m e s , or i n periods with p a r t i c u l a r l y f r e q u e n t e x t r e m e s . Where ade- q u a t e historical i n f o r m a t i o n i s e x t a n t , t h e p r e d i c t i o n s c a n be t e s t e d a g a i n s t histori- cal a c t u a l i t y .

As a n example of t h e p r e d i c t e d i m p a c t from a single, isolated e x t r e m e n-e c a n predict t h a t in t h e cool s u m m e r of 1782, f a r m s l o c a t e d above 300 m ( s e e Figure 2) would h a v e experienced failed o a t s h a r v e s t s . T h e r e is s o m e confirmation of t h i s from a c o n t e m p o r a r y a c c o u n t for t h e high-lying parish of Lauder which r e p o r t s t h a t

"It was t h e end of December before t h e h a r v e s t was finished, a f t e r a g r e a t p a r t of t h e c r o p was destroyed by frost a n d snow. None of t h e f a r m e r s could p a y t h e i r r e n t ; s o m e of t h e m l o s t tn-o h u n d r e d t o five h u n d r e d pounds s t e r l i n g " (Statistical Account of Scotland, 1791-99). T h e r e w e r e s o m e f a r m b a n k r u p t c i e s , with t h e subse- q u e n t a m a l g a m a t i o n of holdings, b u t unlike t h e effect of successive e x t r e m e s in t h e 1690s, t h e parish r e t u r n s for t h e S t a t i s t i c a l Account r e p o r t e d l i t t l e sign of lasting h a r d s h i p in t h e 1790s r e s u l t i n g f r o m t h a t single dismal s u m m e r in t h e p r e c e d i n g decade.

As for t h e c l u s t e r s of consecutively coo1 s u m m e r s , t h r e e would h a v e c a u s e d c o n s e c u t i v e failure above 300 m: 1674-75, 1694-95 a n d 1816-17. More s u b s t a n t i a l r u n s of f a i l u r e would h a v e o c c u r r e d a t h i g h e r levels. For e x a m p l e , above 340 m failure would theoretically h a v e o c c u r r e d i n eleven successive y e a r s from 1688-99 (Figure 2). This elevation appr-oxinlately m a t c h e s t h e a c t u a l u p p e r limit of o a t s cultivation in t h e s e v e n t e e n t h c e n t u r y , s o we can hypothesize t h a t t h e h i g h e s t a r a b l e f a r m e r i n s o u t h e r n Scotland saw failure for 11 c o n t i n u o u s y e a r s in t h e 1690s. In f a c t , a c o m p a r i s o n of t h e m a n u s c r i p t P o n t m a p s dating f r o m a b o u t 1596 with t h o s e of t h e Military Survey of Scotland of 1747-55 i n d c a t e s t h a t few of t h o s e high-lying f a r m s survived: of 32 r e c o r d e d in about 1600, only 10 r e m a i n e d i n t h e

2 ^<-

_L. ^f

'7 c ' a .

G g L

ZCR?

3 .C

a 1 2

'pT

C

rci

.5

-6

bii c

L 2 u '

((anal eas anoqe sJaiauJ) apna!alv

next c e n t u r y .

Less immediately marked b u t probably as enduring in t h e i r effects were t h e periods of more frequent (though s c a t t e r e d ) extremes. The l a t e n i n e t e e n t h cen- tury i s an appropriate example. For this period o u r calculations (Figure 2) point t o harvest failure a t elevations exceeding 310 m for 5 years o u t of t h e 16 between 1877 and 1892. A t these high levels adverse weather and depressed prices were reflected in t h e long-term transfer of arable t o p e r m a n e n t grassland and rough pasture. Offi- cial annual acreage r e t u r n s for t h e region reveal a 5 p e r c e n t reduction in t h e a r e a under crops and grass between 1880 and 1885, a n d reductions of about 1 p e r c e n t every five y e a r s from 1885 t o 1900.

I t

is n o t t h e aim of this paper t o describe t h e s e historical i m p a c t s in any detail. The complicated t a s k of disentangling t h e relative roles of climate, economic and social factors is a m a t t e r for more lengthy t r e a t m e n t elsewhere. Yet it i s apparent from the preceding discussion t h a t , by r e f e r e n c e t o a long r u n of i n s t r u m e n t a l weather data t h a t have been reformulated into' altitudes of crop failure, i t is possible t o identify for a n y particular year o r period, t h e a r e a s m o s t seriously affected by 1;ariations in a c c u m u l a t e d t e m p e r a t u r e .

4. A Risk M a c e of Crop F- dure

With increasing elevation, t h e decrease in t e m p e r a t u r e clearly imposes a g r e a t e r r e s t r a i n t on cultivation, increasing t h e probability of i n a d e q u a t e a c c u m u - lated warmth and crop failure. In an e a r l i e r paper ( P a r r y , 1976) we had assumed annual totals of accumulated warmth t o be normally distributed, a n d found a strongly nonlinear relationship between altitude and risk of c r o p failure, t h e proba- bilities increasing almost exponentially a t certain heights (Figure 3). Subsequently we r e f e r r e d t o this as an a s s u m e d "risk surface" and emphasized t h a t o n e impor- t a n t effect of changes in climate could be t o change t h e location a n d inclination of this risk surface (Carter a n d P a r r y , 1984). We c a n now- discard t h e assumption of normality and, by considering t h e r e a l surface of risk over t h e 323-year period for which we now have data, can e s t i m a t e t h e changes in t h e probability of c r o p failure t h a t have occurred during this long period.

Actual occurrences of crop failure (i.e. years with less t h a n 970 GDD) for t h e period 1659-1961 in southern Scotland were calculated for 10 m intervals. These a r e plotted as frequencies of single a n d two consecutive failures i n Figure 3. The curved lines indicate the corresponding theoretical frequencies for normally distri- b u t e d temperatures. A comparison of a c t u a l and theoretical frequencies indicates a risk surface for single failures t h a t is approximately normal, b u t a distinct clus- tering of cool years results in a s t e e p e r t h a n normal risk surface for consecutive failures. At 340 m (which is approximately t h e limit of cultivation i n t h e region) the r e a l frequency of consecutive failures is m o r e t h a n double t h a t of t h e assumed frequency. 1n some respects,'then, t h e r e a l risk surface is s t e e p e r t h a n expected.

5. Delimiting High-Risk Areas -

I t is also possible to delineate, on t h e basis of this long r u n of d a t a , a high-risk zone in which oats is near its physiological limit and where probabilities of failure a r e very high. lsopleths of c r o p failure frequency reveal t h e d s t r i b u t i o n of these a r e a s (Figure 4). For t h e p r e s e n t we shall adopt the frequencies of l-in-10 and 3 - in-50 a s delineating the upper a n d lower edges of t h e high-risk zone. Ideally the choice of frequencies would be based empirically upon behavioral surveys a t the farm level. But, whatever a r e t h e critical frequencies for certain farming deci- sions, t h e effect of altitude on levels of risk is m u c h the same. For example, on t h e gentle slopes of t h e southern p a r t of t h e study a r e a t h e probability of c r o p failure doubles over a &stance of only about 5 km (Figure 4).

St. Abb's

I ,

. ..

. . '

. ,. .. ^' :.,.. . ::; ,-;:;: : ,.'.

- .:..=: :.<,. Moorland

1970

.,.-.;-.>:.;

. .

⁰ -

. , . - ²

- .

^{4 6 8 1 0 k m}

Fig.

4. lsopleths of actual frequency of crop failure in s o u t h e r n Scotland a s defined by years with less t h a n 970 GDD. Figures in p a r e n t h e s e s indicate a c t u a l f r e q u e n c y of 2 consecutive failures.

6. Changes in the F'requency of Crop Failure

The risk isopleths of 1-in-10 and 1-in-50 a r e average frequencies derived from t h e 323-year record. However, i t is clear from Figure I t h a t a c c u m u l a t e d tempera- t u r e s have varied greatly from one period to a n o t h e r , and Figure 3 i n d c a t e s t h a t these would have produced significant spatial shifts of t h e limit of crop failure. I t follows t h a t t h e high-risk zone is not static b u t , depending on t h e time-scale of study, apparently shifts from year t o year, decade t o decade, a n d c e n t u r y t o cen- tury. A perturbation in t h e climate can t h u s be expressed a s t h e shift of s u c h a risk zone.

To evaluate t h e effect of t e m p e r a t u r e variations t h a t have o c c u r r e d over t h e past 300 y e a r s , we have determined t h e risk surface a n d high-risk zone for cool a n d warm 50-year periods in t h e r e c o r d (1661-1710 a n d 1931-80, respectively), a n d have analyzed t h e i r shift between t h e s e periods.

The shift of the assumed risk surface is considerable, as illustrated by t h e curves in Figure 5. Furthermore, t h e shift of real frequencies (plotted as points) is g r e a t e r still due to t h e higher-than-expected failure frequency in t h e cool period c o n c u r r e n t with fewer-than-expected failures in t h e warm period.

The altitudinal movement of t h e high-risk zone exceeds 85 m, such t h a t t h e line of 1-in-50 frequency for t h e r e c e n t u-arm period lies above even t h a t of t h e 1- in-10 frequency for the cool period, a t t h e nadir of t h e so-called "Little Ice Age". In geographical t e r m s , t h e location of this zone has been radically altered (Figure 6).

Ghile i n t h e l a t e seventeenth century a substantial proportion of t h e foothills (above a b o u t 280 m ) were submarginal to the cultivation of oats, t h e c l i m s t i c limit of cultivation for he modern period stands on average a t 365 m , representing

i

an additional 150 krn of potentially cultivable land.

7 . Conclusions

We have considered elsewhere t h e possible connection between changes of cli- m a t e and changes in t h e use of marginal land (Parry, 1978). Those connections were analyzed on the basis of estimated 50-year averages of t e m p e r a t u r e , t h e argu- m e n t being t h a t long-term changes in climate were t h e changes t h a t , if any, had a n enduring economic effect. However, t h e present analysis of yearly data based on mean monthly temperatures has revealed t h e importance of t h e short-term event, particularly of extreme years. I t has emphasized t h a t an i m p o r t a n t path of i m p a c t from change in average climatic conditions is a change in t h e frequency of e x t r e m e events. Changes in this frequency can be expressed in t e r m s of a shift of the risk surface or of critical boundaries of risk.

M-e have n o t sought to establish these critical levels empirically. That remains t o be done, b u t t h e r e a r e grounds for accepting t h e I-in-50 frequency of crop failure as an approximation of t h e limit t o viable c e r e a l farming in t h e study region. For example, its isopleth for 1931-50 coincides ~ l t h t h e present limit of cul- tivation, or "moorland edge"; a fairly.stable boundary t h a t reflects an a d j u s t m e n t of agriculture t o prevailing economic a n d environmental conditions, and an adjust- m e n t t h a t operates on a decadal r z t h e r than an annual or secular scale.

If t h e r e were a simple causal relationship between climatic risk and the cul- tivation limit then, c e t e r i s parikus, w e v:ould expect both to have shifted in sym- pathy. Not surprisingly t h e actual relationship is far from simple a n d t h e r e a r e many intervening factors. N ~ v e r t h e l e s s , the shifts of risk level and grovrth poten- tial (or of o t h e r derived parameters t h a t have not been considered h e r e ) c a n be taken as a p r e h c t i o n of impact on agriculture; a prediction t h a t c a n be tested against historical records and then, if necessary, reformulated. Subsequently i t should be feasible t o improve our predictions of i m p a c t s from possible f u t u r e

Altitude (meters above sea level)

Fig. 5. Differences in t h e risk s r ~ r l a c e of crop failure for t h e cqol (1601-1710) and warm (1931.-00) 50-year pcriods in sout,llern Scotlar.~l. Shaded a n d st,ipplcd areas d e n o t e " h i g h - r i s k z o n e s .

- N -

~1 in 1 0 2 lsopleths of 1-in-10 and 1-in-50 frequency UPPER ME RSE -1 in 50- of crop failure, 1661 -1 710

,--I in 10-0 lsopleths of 1-in-10 -4 in

50--

and 1-in-50 frequency

of crop failure, 1931--80

-

0

2

4 6 8 1 0 k m

Fig. 6. Locational s h i f t of a high-risk zone between t h e cool (1661-1710) a n d w a r m (1931-80) periods. Risk is expressed a s frequency of o a t s c r o p failure.

c h a n g e s of c l i m a t e by expressing t h e m a s c h a n g e s in t h e frequency of e x t r e m e e v e n t s a n d , t h u s , a s c h a n g e s in level of risk. . One a d v a n t a g e of t h i s a p p r o a c h is t h a t , a s a n adaptive m e a s u r e , a g r i c u l t u r a l s u p p o r t p r o g r a m s could be r e - t u n e d t o a c c o m m o d a t e a c c e p t a b l e levels of risk by a d j u s t i n g s u p p o r t levels t o m a t c h t h e c h a n g e in risk. More g e n e r a l l y , we m a y c o n c l u d e t h a t i f c h a n g e s of r i s k a r e a n i m p o r t a n t possible c o n s e q u e n c e of c l i m a t i c c h a n g e , t h e n we n e e d t o m e a s u r e t h e f r e q u e n c i e s of o c c u r r e n c e of e x t r e m e e v e n t s u n d e r p r e s e n t ( n o r m a l ) c l i m a t i c con- ditions a n d t o u s e t h e s e f r e q u e n c i e s a s a base upon which t o s u p e r i m p o s e t h e effects of a possible f u t u r e c l i m a t i c c h a n g e , t o o b t a i n modified f r e q u e n c i e s of o c c u r r e n c e of s u c h a n o m a l i e s .

REFERENCES

Carter, T.R., and Parry,

M.L.:

1954, 'Strategies for Assessing Impacts of Climatic Change in Marginal Areas',

Proceedings of t h e 2 n d Nordic S p . p o r i u m o n CZimatic Change, B o c k h o l m

(in press).

Edwards, C.: 1978, 'Gambling, Insuring and t h e Production Function', Agric.

Econ.

Res.

30, 25-28.

Jutikkala, E.: 1955, 'The Great Finnish Famine in 1696-?',

S c a n d . Econ. Hist. R e v .

3, 48-63.

Manley, G.: 1945, 'The Effective Rate of Altitudinal Change in Temperate Atlantic Climates',

Geogrl. R e v .

35, 408-417.

Manley, G.: 1951, 'The Range of Variation of the British Climate',

Geogrl.

J. 117, 43-68.

Manley, G.: 1953. 'The Mean Temperature of Central England, 1698-1952',

Quart.

J.

R . Met. Soc.

7 9 , 242-261.

Manley, G.: 1974, 'Central England Temperatures: Monthly Means 1659 t o 19?3',

Q u a r t .

J.

R. Met. Soc.

100, 389-405.

Kenrman, J.E.: 1980, 'Climate Change Impacts on t h e Growing Season of t h e North American Corn Belt',

B i o m e f e o r o l o g y

7, 128-142, Supplement t o

/nt .

J.

R i o m e f e o r .

24.

Nuttonson. M.Y.: 1955,

m e a t - C Z i m a t e Relationshzps a n d the USE of Phenology

in

Ascertaining t h e Thermal a n d Photo- Thermal R e q u i r e m e n t s of Wheat,

h e r . Inst. Crop Ecology, Washington.

Parry, M.L.: 1975, 'Secular Climatic Change a n d Marginal Agricult.ure',

P a n s . h t , Br. Geog. 64,

1-18.

Parry, M.L.: 1976, 'The Significance of t h e Variability of S u m m e r Yiarmth in Upland Britain',

Weather

31, 212-217.

Parry, M.L.: 1975,

CZimatic L7uznge, Agriculture a n d S e t t l e m e n t ,

Dawson.

Perry, P.J.: 1974,

B r i t i s h f i r m i n g

in

t h e Oreat Depression,

1870-1914, Newton

Abbott.

P e a r s o n , K G . : 1973, ' S n o ~ ~ s t o r m s in S c o t l a n d , 1782-86', F e a f h e r 28, 195-201.

Royal Commission: 1883, R o y a l C o m m i s s i o n o n

t h ~

D e p r e s s e d C o n d i f i o n s o f A g r i c u l - t u r a l h t e r e s t s ( t h e I h c h m o n d C o m m i s s i o n ) , Cmnd. 2778.

7he S a t i s t i c a l A c c o u n t o f S o t l a n d : 1791-99, Sir J o h n Sinclair ( e d . ) , Edinburgh.

Williams, G.D.V., a n d Oakes, W.T.: 1970, 'Climatic R e s o u r c e s for Maturing Barley a n d Wheat in Canada', in Hage, K.D. a n d Reinelt,

E.R.

(eds.). E s s a y s o n M e t e o r o l o g y a n d C l i m a t o l o g y :

h

H o n o r o f R L c h m o n d

M:

L o n g l e y , Stud. Geogr. Monogr. 3, D e p a r t m e n t of Geography, University of Alberta, E d m o n t o n , Canada, pp.

367-385.