Impacts of climate variability and change on seasonal drought characteristics of Pakistan

Assessment of the influence of climate variables on drought characteristics is important for adaption to changing pattern of droughts due to climate change. The objective of this study is to assess the changing characteristics of droughts due to climate variability and change during two major cropping seasons (Rabi and Kharif) for the period 1901-2010 over the diverse climate of Pakistan. The gauge-based gridded precipitation and temperature data with a spatial resolution of 0.5 degrees is used for the reconstruction of droughts using standardized precipitation evapotranspiration index (SPEI). The temporal variations in droughts and their relationships with precipitation and temperature are assessed using a 50-year moving window with a 10-year time step. The annual maximum series (AMS) approach is used to estimate the return periods of seasonal droughts and the modified Mann-Kendal trend test is applied to assess the significance of trends in climate variables and drought index. The results showed that drought severity is increasing in the predominantly arid and semi-arid regions for both cropping seasons, while it is decreasing in western disturbance (WD) influenced high winter precipitation region during Rabi season. Temperature is found as the dominating factor for defining droughts in arid and semi-arid regions while the precipitation in WD influenced region. An increase in temperature in the range of 0.001 to 0.025 degrees C per year and almost no change in precipitation have caused decreases in Rabi SPEI in the range of -0.011 to -0.025 per year in the arid region. On the other hand, increases in precipitation in the range of 1.01-2.0 mm/year have caused increases in Kharif SPEI in WD influenced region in the range of 0.016-0.02 per year. However, rises in temperature in most part of the country has caused an increase in drought frequency in both seasons in the areas where droughts are less frequent. The results indicate that rising temperature due to global warming would increase drought severity and frequency in most part of the predominantly arid country.