Abstract:
Medium range (~7 days) forecasts of agricultural and hydrologic droughts can help in decision making in agriculture and water resources management. India has witnessed severe losses due to extreme weather events during recent years and medium-range forecasts of precipitation, air temperatures (maximum and minimum), and hydrologic variables (root zone soil moisture and runoff) can be valuable. We evaluated skill of the Global Ensemble Forecast System (GEFS) reforecast of precipitation and air temperatures using retrospective data for the period of 1985-2010. We found that the GEFS forecast showed better skill in the non-monsoon season than in the monsoon season in India. Moreover, skill in temperature forecast was higher than that of precipitation in both the monsoon and non-monsoon seasons. The lower skill in forecasting precipitation during the monsoon season can be attributed to representation of intraseasonal variability in precipitation from the GEFS. Among the selected regions, the north, northeastern, and core monsoon region showed relatively lower skill in the GEFS forecast. We corrected temperature and precipitation forecasts from the GEFS using the Q-Q mapping and linear scaling, respectively. Bias corrected forecasts for precipitation and air temperatures were improved over the raw forecasts. We evaluated the influence of corrected and raw forcings on medium-range soil moisture, drought, and runoff forecasts. Our results showed that due to high persistence, medium-range soil moisture forecasts are largely determined by the initial hydrologic conditions. Bias correction of precipitation and temperature forecasts does not lead to significant improvement in the medium-range hydrologic forecasting of soil moisture and drought. However, bias correcting raw GEFS forecasts can provide better predictions of the forecasts of precipitation and temperature anomalies over India.