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Discussion papers
https://doi.org/10.5194/hess-2018-642
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2018-642
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Jan 2019

Research article | 17 Jan 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

Spatiotemporal Changes in Aridity of Pakistan during 1901–2016

Kamal Ahmed1,2, Shamsuddin Shahid1, Xiao-Jun Wang3,4, Nadeem Nawaz2, and Najeebullah Khan1 Kamal Ahmed et al.
  • 1Faculty of Civil Engineering, Universiti Teknologi Malaysia (UTM), Johor Bahru, 81310, Malaysia
  • 2Faculty of Water Resource Management, Lasbela University of Agriculture, Water and Marine Sciences, Balochistan, 90150, Pakistan
  • 3State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing Hydraulic Research Institute, Nanjing, 2100292, China
  • 4Research Center for Climate Change, Ministry of Water Resources, Nanjing, 210029, China

Abstract. The changing characteristics of aridity over a larger spatiotemporal scale have gained interest in recent years due to climate change. The long-term (1901–2016) changes in spatiotemporal patterns of annual and seasonal aridity during two major crop growing seasons of Pakistan, Kharif and Rabi are evaluated in this study using gridded precipitation and potential evapotranspiration (PET) data. UNESCO aridity index was used to estimate aridity at each grid point for all the years between 1901 and 2016. The temporal changes in aridity and its associations with precipitation and PET are evaluated by implementing a moving window of 50-years data with 11-year interval. The modified Mann Kendall trend test is applied to estimate unidirectional change by eliminating the effect of natural variability of climate and the Pettitt’s test is used to detect year of change in aridity. The results reveal that climate over 60 % of Pakistan (mainly in southern parts) is arid. The spatial patterns of aridity trends show a strong influence of the changes in precipitation on aridity trend. The increasing trend in aridity is noticed in the southeast where precipitation is low during Kharif while a decreasing trend in Rabi season in the region which receives high precipitation due to western disturbances. The annual and Kharif aridity are found to decrease at a rate of 0.0001 to 0.0002 per year in northeast while Kharif and Rabi aridity are found to increase at some locations in the south at a rate of −0.0019 to −0.0001. The spatial patterns of aridity changes show a shift from arid to the semi-arid climate in annual and Kharif over a large area while a shift from arid to hyper-arid region during Rabi in a small area. The most of the significant changes in precipitation and aridity are observed in the years between 1971 and 1980. Overall, aridity is found to increase in 0.52 %, 4.44 %, and 0.52 % area and decrease in 11.75 %, 7.57 %, and 9.66 % area for annual, Rabi and Kharif seasons respectively during 1967–2016 relative to 1901–1950.

Kamal Ahmed et al.
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Short summary
The long-term changes (1901–2016) in annual and seasonal aridity in Pakistan and its causes are analyzed in this paper. Gauge-based gridded precipitation and PET data are used to show the spatial and temporal patterns of the changes in aridity over the diverse climate of the country. The present study suggests that the relative influence of precipitation and temperature on aridity determines its trends in the context of climate change.
The long-term changes (1901–2016) in annual and seasonal aridity in Pakistan and its causes are...
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