Investigating the Trend of Long-Term Changes in Wheat (Triticum aestivum L.) and Watermelon (Citrullus lanatus) Water Footprints in Sistan and Baluchestan with Mann Kendall Trend Test

     One of the main problems in arid and semi-arid regions of the country is the lack of water for irrigating agricultural products and other uses. Sistan and Baluchestan province is one of the provinces that is considered as one of the arid and semi-arid regions in Iran that is facing water shortage. The present study aimed at evaluating the trend of changes in water footprint of two crops that is wheat and watermelon as the main crops in Sistan and Baluchestan province. In this way, the changes in water footprint in the two components of blue and green water of products and the cause of these changes under the influence of various factors will be investigated.

     The present study aimed at evaluating the trend of changes in water footprint of two crops that is wheat and watermelon as the main crops in Sistan and Baluchestan province. In this way, the changes in water footprint in the two components of water and green water of products and the cause of these changes under the influence of various factors will be investigated. For this purpose, first the water footprint of these two products were investigated in all cities where they were cultivated in two sections: blue and green water footprint in a 30-years’ time span from 1978 to 2017. Then, by using Mann Kendall Trend Test, the trend of long-term changes was investigated. Water footprint calculations were performed through cropwat and aqua crop software and finally according to the blue and green water footprint formula in Excel.
 

     The results have indicated that the trend of changes in wheat water footprint has been increasing in Sarbaz and Iranshahr.  As for watermelon, this trend has been also increasing in Zahedan and Konarak and this is mainly due to reduced rainfall and yields. The average water footprint of wheat and watermelon in Sistan and Baluchestan province has been reported to be 2134.9 and 318.1, respectively. Moreover, the share of blue and green water for two crops of wheat and watermelon has been reported to be 1773, 361.9 and 291.7, 26.5 respectively. The results obtained in this study are consistent with Karandish's research (Kardashian, 2018). The 30-years trend of Mann Kendall method calculated water footprint in three sections of blue green and total water, as well as for yield and rainfall. The results of trend finding for both wheat and watermelon at 95 and 99% levels showed that the yield of watermelon in Nikshahr, Chabahar and Khash counties had an increasing trend and this reduced the blue water footprint and consequently reduced the total water footprint of the crop. Wheat crop is a more effective factor and with the changes of its 30-years trend, the water footprint of the crop, especially its green water footprint, has been affected. In Zabol, Iranshahr and Zahedan stations, this issue is quite evident and with the decrease of rainfall trend, the green water footprint of the crop has decreased.

     The results show more water footprint of wheat than watermelon, which is due to the high yield of watermelon versus wheat.  In comparing the green and blue water footprints of the crops, the results show a greater share of green water footprints in the wheat crop than the watermelon crop, which is also due to the length of the growing season and the date of cultivation and harvest of wheat and more use of rainwater resources. Evaluating the trend of change with Mann Kendall Trend Test indicates an increase in yield and a decrease in rainfall in the 30 years studied in two places, which has increased the blue water footprint and reduced the green water footprint of crops.

     The corresponding author gratefully Acknowledgements the financial support from University of Zabol (Grant No. 9719-21). We would like to thank the anonymous reviewer for very helpful comments and suggestions of the manuscript.