Nonlinear Analysis of Hydroclimatic Variability in Pakistan Using ITA and IPTA Methods

The impacts of climate change on hydroclimatic variables (HV) in the form of untimely rainfall or increasing temperature are well known and of great concern. This paper aims to analyse trend variations and identify the possible intrinsic nonlinear impact of HV on one another. For this purpose, trend variations are assessed for monthly temperature, precipitation, evapotranspiration, and river flow at the Chitral River at Chitral and the Indus River at Gilgit and Tarbela (river flow only), Pakistan, using the Mann–Kendall (MK), Sen’s slope, and nonparametric approaches: innovative trend analysis (ITA) and innovative polygon trend analysis (IPTA). The IPTA approach specifically examines the potential intrinsic nonlinear contribution of HV to the hydroclimatic cycle using statistical quantities average (AVG) and standard deviation (STD) in this paper. Moreover, MK analysis identified a trend in 20 out of 108 months, while ITA identified trends for the majority of the 95 months. ITA indicated impacts of temperature and precipitation on river flow during monsoon at Chitral and Gilgit, respectively, while their mixed impacts are observed post-monsoon at both stations. Overall, IPTA indicates uniformity in the behaviour of evapotranspiration with temperature at Chitral and Gilgit. Furthermore, STD polygons indicated possible impacts of temperature and precipitation in enhancing the river flow at the beginning of and during the monsoon at Gilgit, respectively. Additionally, IPTA plots of both AVG and STD reveal the strong seasonal pattern of actual river flow variation at all stations. These results will be beneficial for predicting irregular trends in HV for adapting climate change mitigation technology for urban, agriculture, and water resource planning sectors.

Graphical abstract