Spatio-Temporal Distribution of Drought and its Characteristics over Pakistan

Abstract

The drought is among the most devastating climatic hazards whose effects remain for years. This study provides complete characteristics and assessment of drought in the country and surrounding regions. The long-term (1951-2016) observational gridded data (0.5°x0.5°) of precipitation is used along with soil moisture. The present work focuses on drought and precipitation climatologies over South Central Asia (SCA), their trends over Pakistan, performance evalutaion of fifteen drought indices to monitor drought along with the development of drought hazard maps of Pakistan, and lastly, shifting of agro-climatic zones, their drought vulnerability and sensitivity of evapotranspiration in these agro- climatic zones. To investigate the inter-dependence of precipitation and drought recurrence in the SCA region, the precipitation and drought climatology have been investigated during 1951-2010. Five statistical tests were employed to determine the trends, randomness and magnitude of a trend at 95% significance level on the monthly and annual scale. The drought of 1971 and 2000-2002 were the extreme droughts observed in SCA region, whereas the drought of 1952 was the most severe in Pakistan. Furthermore, the trends of precipitation, temperature, and evapotranspiration have been identified on the monthly, seasonal and annual basis for different regions of Pakistan. Results show that the annual rainfall has significantly increased in Punjab by 2.45mmyr-1 and Khyber Pakhtunkhwa (KP) by 1.55mmyr-1. Similarly, the highest increase in annual mean maximum and minimum temperature is observed in Balochistan (0.021°Cyr-1 and 0.023°Cyr-1) and decreased of -0.011°Cyr-1 in Gilgit-Baltistan and -0.034°Cyr-1 in KP respectively. Evapotranspiration has significantly decreased in Punjab by -0.43mmyr-1 and increased in Balochistan by 0.90mmyr-1. Annual country analysis shows that maximum temperature is increasing at the rate of 0.007°Cyr-1 and minimum temperature is decreasing at -0.006°Cyr-1. Many indices have been developed, and are being used around the world to monitor drought since a single index does not provide complete information regarding xii drought. Therefore, the comparison of fifteen different drought indices has been carried out to identify the best indices to monitor drought in Pakistan. Their performance and efficiency are evaluated by using different statistical tests for each index. The four indices namely; standardized precipitation index (SPI), standardized precipitation evapotranspira- tion index (SPEI), Reconnaissance drought index (RDI), and deciles index (DI) are more suitable to monitor droughts in Pakistan. Furthermore, the drought frequency, category and types of droughts have also been investigated in this research work. The observed and Global Precipitation Climatology Centre (GPCC) precipitation along with soil moisture data of Climate Prediction Centre (CPC) are used to identify the drought period and duration. Six worst drought years were observed during 1952, 1969, 1971, 2000, 2001 and 2002 over Pakistan where two third of the country was affected. The drought hazard index is developed to prepare the drought hazard map of Pakistan. Five drought hazard classes have been defined and the results indicate that out of 145 districts of Pakistan, 19 districts are extremely, 24 are highly, 56 moderately, 33 low and 13 very low vulnerable to drought. The study also identifies the shifting of agro-climatic zones and their vulnerability towards drought in Pakistan. The results show that 87% of the country geographical area lies in extremely arid to semi-arid climate. The maximum decrease of 8% and increase of 5% in the area are observed in extremely arid and humid zone over the past 30 years (1981-2010) respectively. The analysis shows that intense and severe droughts have been observed in extremely arid zones, whereas the frequency of mild to moderate drought is more in semi-arid zones. A significant increase in annual precipitation has been observed in arid regions (0.83 mmyr-1), whereas the maximum temperature has increased by 0.014°Cyr-1 and 0.018°Cyr-1 in extremely arid and humid regions, respectively. Sensitivity of evapotranspiration (ET) due to percentage change (±20%) in meteorological parameters has also been investigated in different agro-climatic zones of Pakistan. Total ET demands have increased in all the agro-climatic zones with a maximum of 16.9% for temperature and 6.1% for wind speed in extremely arid, 16.4% for net radiation in humid and decreased of -10.9% for vapor pressure in extremely arid zones, respectively.