Drought analysis under changing precipitation extremes in the Upper Indus Basin Pakistan

Upper Indus Basin (UIB) represents three vast mountain ranges of the Himalayan-Karakoram-Hindukush (HKH) ranges in Pakistan. Recent regional warming trends even at high altitudes have confirmed the alteration of the hydrological cycle attributed to global warming. This warming tendency affects the monsoon precipitation in terms of wetting and drought in Pakistan with unprecedented intensity, causing either severe flooding or episodic drought. Therefore, it is worth observing the recent spring and summer monsoon changes in extreme precipitation and drought severity throughout Pakistan. The present study examined 8 precipitation indices in the past 50-year period (1971–2020) (stretched to two data periods) using Mann–Kendall and Sen’s method to investigate the direction and magnitude of the observed trends. For drought estimation, the Percentage Normal (PN), and Percentage Deviation (PD) indexes were analyzed. We observed that spring and summer wet days significantly increased in the central-eastern (Kakul, Kotli, Jhelum) and western (Cherat, Chitral, Peshawar) regions in the 1st data period but significantly decreased in areas including the southern region in the 2nd data period. We further observed the high-intensity precipitation days (R10, R20) in the same seasons. The intensity of summer R20 was much stronger throughout Pakistan in the 1st data period which reduced significantly during the 2nd data period in northern and southern regions. We extended the circle of investigation to very heavy and extreme precipitation (R30 and R50). The intensity of R30 and R50 in summer followed the same pattern as observed for R10 and R20. However, R30 and R50 in pre-monsoon significantly increased in the northern, east-western, and south-eastern regions during the 2nd data period. Similarly, drought analysis proposed an extreme wetting tendency in the western UIB and lower areas of southern Punjab in the last two decades. Summer monsoons and westerly humid regions also experienced severe drought in terms of heavy and very heavy precipitation extremes. Our results concluded that the most significant changes in precipitation extremes and drought severity occurred with higher intensity and recurring frequency for all indices in spring and summer monsoon during the 2nd data period.