Abstract: Quantifying evapotranspiration and drainage losses is essential for improving irrigation efficiency. The FAO-56 is the most popular method for computing crop evapotranspiration. There is, however, a need for locally derived crop coefficients (Kc) with a high temporal resolution to reduce errors in the water balance. The aim of this paper is to introduce a dynamic Kc approach, based on Leaf Area Index (LAI) observations, for improving water balance computations. Soil moisture and meteorological data were collected in a terraced nectarine (Prunus persica var. nucipersica) orchard in Cyprus, from 22 March 2019 to 18 November 2021. The Kc was derived as a function of the canopy cover fraction (c), from biweekly in situ LAI measurements. The use of a dynamic Kc resulted in Kc estimates with a bias of 17 mm and a mean absolute error of 0.8 mm. Evapotranspiration (ET) ranged from 41% of the rainfall (P) and irrigation (I) in the wet year (2019) to 57% of P + I in the dry year (2021). Drainage losses from irrigation (DR_I) were 44% of the total irrigation. The irrigation efficiency in the nectarine field could be improved by reducing irrigation amounts and increasing the irrigation frequency. Future studies should focus on improving the dynamic Kc approach by linking LAI field observations with remote sensing observations and by adding ground cover observations.

Abstract: Apart from some notable exceptions, the sound governance of transboundary aquifers (coupled or uncoupled to rivers) is seriously lacking in most regions of the world, despite a highly successful 20-year ISARM initiative. The distinction between regions of water abundance (as in the Haute Savoie–Geneva aquifers) and those of water scarcity (\textless1000 m3/an/capita), as in the Rum-Saq aquifer, ought to be a driver for the urgency in adopting sound governance. In the latter regions, however, such an urgent response faces too many hurdles (institutional, financial, and weak capacity). Climate change, one of the global megatrends (among demography, economic shift, resources stress, urbanization, and novel viruses such as COVID-19), will exacerbate the problem in the coming decade and beyond. This chapter provides an critical perspective on the status of this subsurface asset in 570 or so, domestic and transboundary aquifers of the world (self-identified by country experts), while taking full account of their interconnections, or not, with surface waters. This critical perspective will be grounded in two important factors, first the hiatus in adoption by countries of the evolving international water law and guidance on transboundary aquifers (the Draft Articles, which provide legal pathways for collaboration or eventually dispute resolution), and second the framework of the sustainable development goals (SDG) 6 (clean water and sanitation), which countries have committed themselves to with reference to transboundary waters. The critical perspective finds that despite the lack of momentum in adopting formal global norms, sporadic cooperation and collaboration is continuing and is well received, when delivered methodically through the support of international agencies. The findings of the critical perspective are that even if water-related SDGs will have been achieved across the world, it would contribute precious little to meaningful enhancement of governance of transboundary aquifers, unless they have been explicitly addressed in terms that are tangible to decision makers, such as the impact of disregarding them on the current or future national GDP. The onset of a “new socioeconomic normal” in the aftermath of COVID-19 could further defer meaningful progress, taking the example of Latin America, where a 5% decline has been forecast for 2020. With such declines in the finances of governments, attention to shared aquifer resources may well decline even further. Urgent wise reaction to this possibility must be a priority for the professional science-policy community.

Abstract: Competing commercial demands on water resources need to be balanced as the world’s population rises. Generally, groundwater is raised by subsurface dams. In this paper, the geographic information system (GIS) software and a decision-making method were applied. As the first step, the limitations that affect the establishment of the subsurface dam were identified using eliminating criteria by the Boolean logic. Regarding the second step, the most appropriate axis was determined for subsurface dam construction in each of the limits. The analytical hierarchy process (AHP) was applied according to the evaluation criteria in this study. The aim of using AHP was to weigh and prioritize the criteria of the groundwater dam for recognizing appropriate sites. Among various places and regarding the subsurface dam construction, AHP was conducted using a hierarchy process for finding the most suitable sites in the third stage of the decision-making method. Finally, among the ten appropriate sites, cross comparison was drawn by using Decision Expert (DEX), Evaluation based on Distance from Average Solution (EDAS), and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). Compared together (as a process of decision-making), DEX, TOPSIS, and EDAS methods assisted in ranking the most appropriate sites in the final step of subsurface dam pre-selection. A and C axes obtained scores between 1 and 2, among 10 axes according to the numerically ranked locations. Regarding the water shortage issue and better management of the underground water at certain levels, the findings of this study could be useful for the residents of Kajbid-Balaqly Watershed in the dry season. Further, water managers can use the above-mentioned methods for their decisions regarding the proper subsurface dam establishment.

Abstract: Urban flooding in Chittagong City usually occurs during the monsoon season and a rainwater harvesting (RWH) system can be used as a remedial measure. This study examines the feasibility of rain barrel RWH system at a distributed scale within an urbanized area located in the northwestern part of Chittagong City that experiences flash flooding on a regular basis. For flood modeling, the storm water management model (SWMM) was employed with rain barrel low-impact development (LID) as a flood reduction measure. The Hydrologic Engineering Center’s River Analysis System (HEC-RAS) inundation model was coupled with SWMM to observe the detailed and spatial extent of flood reduction. Compared to SWMM simulated floods, the simulated inundation depth using remote sensing data and the HEC-RAS showed a reasonable match, i.e., the correlation coefficients were found to be 0.70 and 0.98, respectively. Finally, using LID, i.e., RWH, a reduction of 28.66% could be achieved for reducing flood extent. Moreover, the study showed that 10%–60% imperviousness of the subcatchment area can yield a monthly RWH potential of 0.04–0.45 m3 from a square meter of rooftop area. The model can be used for necessary decision making for flood reduction and to establish a distributed RWH system in the study area.