Mapping Compound Climate Extremes in Pakistan: A Spatio-temporal Analysis

Abstract

The anthropogenic shifts in the climate have triggered an unprecedented rise in climate extremes which have impacted millions of lives and caused trillions of dollars’ worth of damage. The climate drivers that cause these high impact events are usually spatially or temporally compounded. These compound climate extremes are extreme events that occur simultaneously, in close succession or due to drivers that are not implicitly extreme but become extreme when combined. The impact depends on the vulnerability and exposure of the stakeholders that define the risk. Compound climate extremes are exemplified through hot-dry such as compounding heatwaves and drought or hot-wet extremes such as compounding heatwaves and extreme precipitation. Pakistan is not a new to the occurrence of heatwaves and extreme precipitation however, the compounding of these extremes is a relatively novel field of study. This study aims to identify the spatial and temporal existence of coincident heatwaves and extreme precipitation events, and sequential heatwaves and extreme precipitation events at meteorological stations across Pakistan. The study objectives are to detect and quantify the occurrence of extreme weather events i.e. heatwaves and extreme precipitation, and compound climate extremes by employing daily observational datasets for daily maximum temperatures (˚C) and precipitation (mm). The data is obtained for 47 meteorological stations across Pakistan for the period of 38 years, 1980 to 2017. The study is conducted based on the 95th percentile thresholds of daily maximum temperature and precipitation data at each station to classify heatwaves and Extreme Precipitation events. The classification is done using formulas based on scientific definitions using Microsoft Excel 2019. The events occurrence is quantified for both extremes in Microsoft Excel 2019 and visualized through spatial extrapolation in the form of GIS Maps created using Inverse distance weighted (IDW) interpolation in QGIS. Extreme events are considered coincidently compounding if they occur on the same day and are considered sequentially compounding if extreme precipitation occurs within 7 days of the occurrence of a heatwave event. The analysis finds the occurrence of 24 coincidental and 166 sequentially compounding heatwaves and extreme precipitation events in Pakistan from 1980 to 2017. The study finds that the coincident heatwaves and extreme precipitation events are restricted to the northeastern and northwestern stations of Pakistan, and northeastern stations of Balochistan; these stations are characterized by wet days, high precipitation rates, elevation, and adjacent to mountain ranges. Sequentially compounding heatwaves are spread throughout Pakistan in addition to these stations. All events are the highest in number in the submontane monsoon dominated zone followed by Western Highlands zone. The higher occurrence can be attributed to an increase in evaporation resulting from heatwaves which leads to these compounding extremes. This highlights the orographic uplifting assisted quick convection and moisture convergence at elevated stations for creating the conditions for coincident heatwaves and extreme precipitation events. While convection takes time at stations with lower elevations due to slower convection resulting from a lack of orographic uplifting and from moisture absorbance in the soil due to aridity. Moreover, the findings depict that sequentially compounding extremes have increased in the latter half of the study period at the southern stations of Punjab due to increase in extreme precipitation events and their intensity at these stations. These compounding extremes are especially high risk as compared to isolated extreme events because of the smaller gap between their occurrences which leaves little to no time to respond. Moreover, these events not only cause heatwave associated morbidities and losses and damages, but also lead to pluvial and flash flooding. The occurrence of these events especially in southern provinces, as depicted by the study, highlights the potentially high risk of impact as a consequence of the large population, underdevelopment, pervasive poverty, social inequalities, and crippling infrastructure which increases the exposure and vulnerability of the people to such events. The study is novel and the first of its kind as it analyzes the occurrence of compounding heatwaves and extreme precipitation events using the historical temperature and precipitation data. The study also highlights the specific regions where compounding climate extremes are prevalent. This research is significant to climate knowledge and can be helpful in climate risk assessments in terms of hazards along with contributing to the local planning and development for addressing these risks in the future to build resilience.