Exploring trends and variability of climate change indices in the agro-ecological zones of Pakistan and their driving mechanisms

Anthropogenic climate change induced weather and climate extremes have led to frequent heat waves, droughts and floods threatening water resources and food security for an agricultural country like Pakistan. Despite their significance, the trends and variability of extreme temperature and precipitation indices and associated large-scale drivers in the agro-ecological zones (AEZs) of Pakistan remain unknown and need urgent attention because of abrupt climate change. The present study documents the spatiotemporal variations of climate change indices together with the elevation-dependent variability trends over various AEZs in Pakistan for the period of 42 years (1979-2020). Nonparametric Mann-Kendall (MK) and Sen's slope (SS) estimator tests have been employed for trend estimation. Results indicated linearly increasing (warming) and statistically significant trends in Tmean, TNx, WSDI and TR20 whereas significant decreasing (cooling) trends in cool nights (-1.73 days<middle dot>decade-1) and cold spells (-1.28 days<middle dot>decade-1). The spatial distribution of temperature indices trends depicts robust warming over southwestern and central zones while cooling trends over northern zones. Regarding precipitation extremes, all indices have shown increasing (wetter) trends with a significant increase in PRCPTOT and RX5day. The stations in northern and subhumid AEZs received more precipitation compared to other zones. Elevation-dependent trends in temperature indices exhibited a statistically significant positive (negative) relationship with cold (warm) tails. Most of the extreme precipitation indices have a weak, but positive association with elevation except SDII. The weakening of South Asian subtropical upper-level jet by a high-pressure system over northeast Pakistan resulted in amplified land surface temperatures. However, the spatial patterns of zonal winds indicate a trough over Pakistan's southern and central parts, with warmer sea-surface temperature, low sea-level pressure and easterly anomalies, favour moisture transport and precipitation in Pakistan. The outcomes of present study will be useful in addressing various climate-induced disasters occurring in various AEZs of Pakistan. The probability distribution of temperature and precipitation extremes depicts more warming and amplified precipitation over the most of AEZs of Pakistan, calling for comprehensive investigation of the factors influencing their variation. Temperature extremes are more pronounced in the southwestern and central regions while precipitation extremes in the northern and subhumid regions of the country. It is deduced that due to significant surge in extreme indices, the country is vulnerable to extreme weather events especially floods, heatwaves and droughts. image