Estimation of Weekly Soil Moisture and Agricultural Drought for Future Periods Using DSSAT Model (Case Study: Birjand Plain)

Soil moisture is a determining parameter in many complex environmental processes and plays a decisive role in the occurrence of agricultural drought. For this purpose, in this study, using soil moisture data estimated by DSSAT model and Fifth Climate Change Report data, agricultural drought was determined by soil moisture deficiency index for future periods of (2015-2045) and (2045-2075) and they were compared with baseline period (1975-2005). The climatic data were estimated using GCM models and two emission scenarios RCP4.5 and RCP8.5 and they were scaled using LARS-WG model and entered into DSSAT model. Finally, using soil moisture data of 30 and 60 cm depths, agricultural drought was evaluated using SMDI index. Climate change results showed that the minimum and maximum temperature and precipitation will increase in the next period compared to the baseline period, and the RCP8.5 scenario estimated a higher temperature and lower precipitation than the RCP4.5 scenario. Weekly soil moisture decreased for future periods compared to the baseline and soil moisture values in RCP4.5 scenario were higher than the ones in RCP8.5 scenario. Also, weekly soil moisture changes at different irrigation levels in the base period are less than those in the future. Estimated values of SMDI drought index by RCP4.5 scenario at 0-30 depth in period of 2015-2045 are more negative and drought than the ones in future period 2045-2075; while the future period of 2045-2015 in RCP8.5 scenario has a better situation. The SMDI drought indices of 30-60 cm depth in both scenarios for the upcoming 2015-2045 period show lower values than the ones in 2045-2075 future period. The RCP4.5 scenario estimates a higher SMDI drought index than the RCP8.5 scenario.