Abstract
Decreases in climatic water availability (CWA) and increases in crop water demand (CWD) in the background of climate change are a major concern in arid regions because of less water availability and higher irrigation requirements for crop production. Assessment of the spatiotemporal changes in CWA and CWD is important for the adaptation of irrigated agriculture to climate change for such regions. The recent changes in CWA and CWD during growing seasons of major crops have been assessed for Iraq where rapid changes in climate have been noticed in recent decades. Gridded precipitation of the global precipitation climatology center (GPCC) and gridded temperature of the climate research unit (CRU) having a spatial resolution of 0.5°, were used for the estimation of CWA and CWD using simple water balance equations. The Mann–Kendall (MK) test and one of its modified versions which can consider long-term persistence in time series, were used to estimate trends in CWA for the period 1961–2013. In addition, the changes in CWD between early (1961–1990) and late (1984–2013) periods were evaluated using the Wilcoxon rank test. The results revealed a deficit in water in all the seasons in most of the country while a surplus in the northern highlands in all the seasons except summer was observed. A significant reduction in the annual amount of CWA at a rate of −1 to −13 mm/year was observed at 0.5 level of significance in most of Iraq except in the north. Decreasing trends in CWA in spring (−0.4 to −1.8 mm/year), summer (−5.0 to −11 mm/year) and autumn (0.3 to −0.6 mm/year), and almost no change in winter was observed. The CWA during the growing season of summer crop (millet and sorghum) was found to decrease significantly in most of Iraq except in the north. The comparison of CWD revealed an increase in agricultural water needs in the late period (1984–2013) compared to the early period (1961–1990) by 1.0–8.0, 1.0–14, 15–30, 14–27 and 0.0–10 mm for wheat, barley, millet, sorghum and potato, respectively. The highest increase in CWD was found in April, October, June, June and April for wheat, barley, millet, sorghum and potato, respectively.
Highlights
The increase in precipitable water vapor in the atmosphere due to rises in temperature has changed the seasonal and geographical distribution of precipitation in many regions of the globe [1,2,3]
The present study was conducted to assess the changes in climatic water availability and irrigation needs in Iraq for the period 1961 – 2013 using global precipitation climatology center (GPCC) precipitation and climate research unit (CRU) temperature data
climatic water availability (CWA) revealed a significant decrease during summer crop growing seasons over the entire of Iraq while a decrease in the west and the southeast during winter crop growing seasons was revealed
Summary
The increase in precipitable water vapor in the atmosphere due to rises in temperature has changed the seasonal and geographical distribution of precipitation in many regions of the globe [1,2,3]. The climatic water availability (CWA), which is the difference between the evaporative demand of a reference crop and the total precipitation, has changed due to the rise in evapotranspiration and the alteration in precipitation. The CWA and crop water demand (CWD) have changed due to the changes in seasonal rainfall pattern and rises in temperature. There is no study so far on detecting/assessing the spatiotemporal changes in CWD and CWA employing long-term precipitation and temperature data and trustworthy methods. The present study aims to evaluate the spatiotemporal pattern in the trends in CWD and CWA of Iraq using MMK tests. The Sustainability 2020, 12, 3437 changes in CWA and CWD would provide valuable knowledge required for long-term management of water resources in Iraq. The “modifiedmk” package available in statistical software R was used in this study for the estimation of Sen’s slope, and MK and MMK test significance
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