6.2 Application One: Climatic changes and scenarios for Wadi Kafrein
6.2.1 Variations in rainfall amounts and intensities
In order to investigate the impact of extreme changes in precipitation amount and intensity, such as those induced by a changing global climate system, extreme years from the climate record were implemented in the model. This new method of approach is one way to overcome the problem of uncertainties in using GCMs. In this approach, the aim is not to predict climate change; rather, the aim is to investigate the impact of variations in precipitation amount and intensity using extreme years (very wet and very dry) as a boundary to predict the impact on the different water components of Wadi Kafrein catchment. Within the same line of reasoning, the impact of temperature increase on runoff generation, evapotranspiration, and recharge were also investigated, but this will be discussed subsequently.
Historical climate data from Wadi Kafrein was retrieved from the records of the Jordanian Ministry of Water and Irrigation (MWI). Daily rainfall values and intensities were analyzed for eight rainfall stations over the time span from 1980 to 2008. The spatial distribution of the stations, which are operated by the MWI, is
Wadi Es Sir annual rainfall 1943-2008
0 200 400 600 800 1000 1200 1400
1943 1945 1947 1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007
Years
Rainfall (mm)
Annual rainfall Long term average
shown in Fig. 4.13 and 6.5 of this chapter. The data of these rain stations were used to prepare several climatic scenarios which simulate the expected precipitation patterns.
The scenarios have been prepared in two steps. The first step was the scenarios being prepared based on the annual rainfall amount and the daily accumulated rainfall. The second step was daily rainfall time series of all scenarios were refined with respect to temporal resolution. This step was possible by statistical analysis of all rainfall events monitored during the period of this research (2007-2009), in which a high temporal resolution of rainfall data is available. From these rainfall events, several rainfall intensity patterns were selected and were used as an index to refine the available daily data, which did not have such a high resolution.
Figure 6.1 shows an example of the data series from one station (Wadi Es Sir Rain station). The annual rainfall amounts are from 1943 to 2008. These values have been calculated from daily data. The long term annual average is 523 mm.
Fig. 6.1: Annual rainfall amounts for Wadi Es Sir Rain station from 1943 to 2008.
Rainfall data series are available from all stations covering the last 30 years. Records preceding the early 1980‟s were kept at only few of the stations. Due to this fact, the available rainfall data from 1980 to 2008 were used in the climatic scenarios. Records dating to 65 previous years were selected for the evaluation of impacts from extreme years (very wet and very dry water years). Two extreme water years, 1991/1992 and 1998/1999, which were the wettest and driest, respectively, were used for the specific years used in the scenarios. Figure 6.1 indicates that the water year 1991/1992 is the wettest year on record while the water year 1998/1999 is the second driest after the 1950/1951 year. Data on 1950/1951 were not available recorded at all rainfall stations; so in order to use the years with maximum data, the 1998/1999 water year was selected and analyzed.
Long term 523 mm
6.2.1.1 Rainfall data preparation and downscaling
The annual and daily approach can be summarized as follow:
1. Daily rainfall data were acquired from all available rainfall stations (operated by MWI/Jordan), distributed between the Jordan Valley (1 station), inside the catchment area (3 stations), and around the catchment area (4 stations), see Fig. 6.5.
2. The available rainfall data were statistically analyzed for every station for the period extending from 1980 to 2008. The annual rainfall amount, number of rainy days, and rainfall depth of every day were considered.
3. Different climatic scenarios which present the possible precipitation patterns were prepared: Wet Year (2 scenarios), Average Year (1 scenario), and Dry Year (2 scenarios). This yielded five main scenarios as shown in Table 6.1 and graphically in Fig. 6.2.
A water year has been considered as a wet year when the annual accumulated rainfall amount of that year is higher than the long term annual average rainfall in at least 25%, while a water year is considered dry when the total accumulated rainfall of that year is less than the long term annual amount in at least 25%. So far, the annual rainfall amount was considered not the daily rainfall depth; therefore, two scenarios for every wet and dry year were considered based on two factors: first, number of the rainy days, second the daily accumulated rainfall amount (rainfall depth, mm/day).
The total daily accumulated rainfall amounts of every station for the whole time series were calculated then the results were grouped as follow:
Number of rainy days with precipitation less than 25mm/day.
Number of rainy days with precipitation between 25 and 50 mm/day.
Number of rainy days with precipitation between 50 and 75 mm/day.
Number of rainy days with precipitation between 75 and 100 mm/day.
Number of rainy days with precipitation more than 100 mm/day.
By combining the annual rainfall amount with the daily rainfall amounts (based on their statistical properties), five scenarios of water years are proposed as shown in Table 6.1. The average year has been selected in which a year with an average long term annual rainfall and an average daily rainfall characteristics. The daily rainfall amounts were calculated and analyzed for all rainfall data since 1980 until 2008 for the eight rainfall stations used in the approach.
Table 6.1: The proposed scenarios based on yearly rainfall amount and daily rainfall depth.
Annual Rain Daily Rainfall amount Scenario ID Description High
High Rainfall Depth Scenario 1-HH Wet year with high daily rainfall depth Low Rainfall Depth Scenario 2-HL Wet year with low daily rainfall depth Average Average Rainfall Depth Scenario 3-Avg Average year with average daily rainfall depth
Low
High Rainfall Depth Scenario 4-LH Dry year with high daily rainfall depth Low Rainfall Depth Scenario 5-LL Dry year with low daily rainfall depth
Fig. 6.2: The proposed climatic scenarios based on yearly rainfall amount and daily rainfall depth.
The available data which have been used in developing the climatic scenarios are in daily bases, but for detailed representation of runoff generation processes; a higher temporal resolution is required. Therefore; the rainfall pattern was studied from the raingauges stations which have been installed in the study area with data records from October 2007 until December 2009 and has a temporal resolution of 5 minutes. The rainfall patterns have been studied for all rainfall events with 5 minutes time step and were categorized as follow:
Events with high intensity in one day: see Fig. 6.3 and 6.4a
Events with step wise precipitation in one day: see Fig. 6.3 and 6.4b
Events with low intensity in one day: see Fig. 6.3 and 6.4c
These patterns represent the way in which rainfall can take place, that is for the same rainfall amount the rain can fall either with high rainfall intensity within few hours (high intensity) or it can fall with low intensity along the day (low intensity) or it can be a combination between high intensity then several hours of no rain and then it rains again (step wise). By combining the annual scenarios presented in table 6.1 with the 5 minutes rainfall patters a total of 15 scenarios were generated as presented in table 6.2.
Table 6.2: The proposed 15 climatic scenarios based on rainfall amount and intensity.
Annual Daily 5 Minutes
High total amount
High Rainfall Depth
High Intensity Scenario HIS Step Wise Scenario SWS Low Intensity Scenario LIS Low Rainfall Depth
High Intensity Scenario HIS Step Wise Scenario SWS Low Intensity Scenario LIS Average total amount Average Rainfall Depth
High Intensity Scenario HIS Step Wise Scenario SWS Low Intensity Scenario LIS
Low total amount
High Rainfall Depth
High Intensity Scenario HIS Step Wise Scenario SWS Low Intensity Scenario LIS Low Rainfall Depth
High Intensity Scenario HIS Step Wise Scenario SWS Low Intensity Scenario LIS
The daily amount differs in every storm event, therefore the storm events were grouped as follow:
Storm event with precipitation less than 25 mm per day
Storm event with precipitation from 25-50 mm per day
Storm event with precipitation from 50-75 mm per day
Storm event with precipitation from 75-100 mm per day
Storm event with precipitation more than 100 mm per day
By combining the daily storm amounts (5 groups) with the precipitation patterns (3 patterns) a 15 pattern index have been produced and the daily rainfall amounts had been downscaled to 5 minutes time step taking in consideration the daily precipitation amounts and the storm events patterns. Every storm event group has a total daily rainfall amount index, from which the given daily rainfall had been downscaled to 5 minutes time step based on the downscaling pattern index as shown in Fig. 6.3.
Fig. 6.3: Daily rainfall downscaling approach using 3 intensities patterns.
By considering the different rainfall intensities patterns, the same rainfall amount can fall in the same day with different intensity per same time step (i.e. 5 minutes). Figure 6.4 shows the different patterns which are proposed for the same daily rainfall amount but different amount per time step.
As the rainfall data were prepared and downscaled based on the above mentioned approach, accordingly this approach has been applied for the eight rain stations data series for the selected scenarios to be simulated. The other important data which are still required before starting the simulation are the climatic parameters (i.e.:
temperature, relative humidity, solar radiation and wind speed). The climatic parameters were collected and interpolated from 5 weather stations distributed between the Jordan Valley and the high lands to the east and are discussed in the coming section.
Downscaling pattern index
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1 31 61 91 121 151 181 211 241 271
5 min Time steps
accumulated rainfall/day
High intensity Stepwise intensity Low intensity
Fig. 6.4: Possible distribution patterns for similar rainfall amounts.
6.2.1.2 Climatic data preparation and interpolation
In this research a complete data set from five weather stations were prepared to be used in the proposed climatic scenarios (Table 6.3). The climatic parameters were collected from two weather stations operated by the MWI and three weather stations operated by the Jordan Meteorological Department (JMD). The spatial distribution of the raingauges and the weather stations is given in Fig. 6.5.
The weather stations are distributed between the Jordan valley in the western side and the high lands to the east of the study area. It has been considered to get the most possible available data spatially and temporally because the variations within the
High intensity
catchment area of Wadi Kafrein are wide. The contradictory and huge variations within short distances require detailed and careful analysis in which the availability and quality of the data play a big role.
Table 6.3: Locations of the weather stations used in the climatic scenarios.
Station Authority Latitude (N) Longitude (E) Altitude (m)
Salt JMD 320 02` 350 44` 796
South Shuna MWI 310 54` 350 38` -160
Sweileh JMD 320 00` 350 54` 1050
Jordan University JMD 320 01` 350 53` 980
Wadi Es Sir (NRA yard) MWI 310 57` 350 51` 900
Fig. 6.5: Weather stations and raingauges used in the climatic scenarios.