بررسی روند تغییرات بلندمدت ردپای آب در محصول گندم (triticum aestivum l.) و هندوانه (citrullus lanatus) در استان سیستان و بلوچستان

یکی از مشکلات اساسی مناطق خشک و نیمه خشک کشور، کمبود آب برای آبیاری محصولات کشاورزی و دیگر مصارف است. استان سیستان و بلوچستان یکی استان‌هایی است که جزو مناطق خشک و نیمه خشک کشور محسوب می‌شود که با مشکل کم‌آبی مواجه است. هدف این پژوهش، ارزیابی روند تغییرات ردپای آب دو محصول گندم (triticum aestivum l.) و  هندوانه (citrullus lanatus)  به‌عنوان عمده‌ترین محصولات مورد کشت در استان سیستان و بلوچستان می‌باشد. برای این منظور، ابتدا ردپای آب این دو محصول در تمامی شهرستان‌هایی که کشت می‌شد، در دو جز ردپای آب آبی و آب سبز به‌صورت 30 ساله از سال 1366 تا 1396 محاسبه شده و سپس با روش روندیابی منکندال، روند تغییرات بلندمدت آن‌ها مورد بررسی قرار گرفت. نتایج نشان داد، روند تغییرات ردپای آب گندم در شهرستان‌های سرباز و ایرانشهر و هندوانه در شهرستان‌های زاهدان و کنارک افزایشی بوده که این عمدتاً به‌دلیل کاهش بارندگی و کاهش عملکرد می‌باشد. متوسط ردپای آب گندم و هندوانه در استان به‌ترتیب 2134.9 و 318.1 مترمکعب بر تن به‌دست آمد که سهم آب آبی و آب سبز به‌ترتیب برای دو محصول گندم و هندوانه 1773، 361.9، 291.7 و 26.5 مترمکعب بر تن به‌دست آمد. در نتیجه، محصولاتی با عملکرد و بهره‌وری پایین و ردپای آب کل بالا برای منطقه مناسب نیست که لازم است در تعیین الگوی کشت منطقه لحاظ گردند.

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

introduction     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.materials and methods     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. results and discussion     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.conclusion     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.acknowledgements     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.