Assessment of changes in water cycles on food production and alternative policy scenarios

The atmospheric branch of the water cycle, although containing just a tiny fraction of the Earth’s total water reserves, presents a crucial interface between the physical climate (such as large-scale rainfall patterns) and the ecosystems upon which human societies ultimately depend. Because of the central importance of water in the Earth system, the question of how the water cycle is changing, and how it may alter in future as a result of anthropogenic changes, present one of the greatest challenges of this century. The recent Intergovernmental Panel on Climate Change report on Climate Change and Water (Bates et al 2008) highlighted the increasingly strong evidence of change in the global water cycle and associated environmental consequences. It is of critical importance to climate prediction and adaptation strategies that key processes in the atmospheric water cycle are precisely understood and determined, from evaporation at the surface of the ocean, transport by the atmosphere, condensation as cloud and eventual precipitation, and run-off through rivers following interaction with the land surface, sub-surface, ice, snow and vegetation. The purpose of this special focus issue of Environmental Research Letters on anticipated changes in the global atmospheric water cycle is to consolidate the recent substantial advances in understanding past, present and future changes in the global water cycle through evidence built upon theoretical understanding, backed up by observations and borne out by climate model simulations. Thermodynamic rises in water vapour provide a central constraint, as discussed in a guest editorial by Bengtsson (2010). Theoretical implications of the

Water scarcity and its impacts on agricultural production and food security are growing concerns worldwide. As the most populous country with a rapidly expanding demand for water and food, China‘s situation in many aspects exemplifies the global picture. Northern China has long been a populous area and an industrial and agricultural base in the country. It is the most serious area of water shortage in China. The total amount of water use increased from 243.7 billion m3 in 1994 to 254.2 billion m3 in 2002. Lack of water has become a big constraint to the development of agricultural production and social economy. Many areas in Northern China have average water resources below 500 m3 per person. With the growing demand for water from agriculture, as well as industries and municipalities, water resources have been exploited excessively. Pollution and environmental degradation, in particular soil and water erosion, have compounded the situation by reducing the availability of usable fresh water.With more frequent droughts enhanced by the changing climate, the potential for additional water supply would decrease. This study intends to reveal the water shortage issues, changes in water cycle and impacts of climate change on the hydrological cycle in Northern China. Firstly, the natural and socio-economic conditions related to the changes in the water cycle as background in Northern China are briefly introduced. The Variable Infiltration Capacity model (VIC-3L) is applied to project the possible changes in water resources, including water supply and demand for the different areas in Northern China under the projected climate change scenarios by Hadley Center‘s regional climate model system-PRECIS. Then, the adaptive capacity to changes in the water cycle is analyzed by assessing the vulnerability of water resources to the climate change under different climatic and socio-economic scenarios. Finally, it is discussed the possible adaptive options related to the sustainable development and utilization of water resources in Northern China, such as optimizing the distribution of water resources, improving the efficiency of water use, enhancing the saving of water use as well as protection and rehabilitation of ecosystems.Key wordsAdaptive capacityclimate changeNorthern Chinavulnerabilitywater cyclewater resources

Mechanisms influencing changes in water cycle processes in the changing environment of the Songnen Plain, China

<p>Yangtze River and Yellow River are the two most important rivers in China. Long-term observation shows that runoff ratio (i.e., runoff/precipitation, denoted as RR) in the headwater of both Yangtze River (HYZR) and Yellow River (HYER) has experienced significant decrease and then increase trend (referred as V-change) during the period 1980-2015. Over the whole period, RR of the HYER shows significant decreasing trend (-0.02/10a, p < 0.05), while it is not significant for the HYZR. Changes in RR in both HYZR and HYER pose great challenge on runoff predication and water management in the downstream. However, driven mechanisms underlying the V-change of RR are still unclear. Here, based on ground-based and remote sensing datasets, both terrestrial and atmospheric water budgets are investigated to understand the evolution of RR in the headwater regions of Yangtze River and Yellow River. Terrestrial water budgets are for evaporation estimation and water cycle analysis. Atmospheric water budgets are used to calibrate the estimated evaporation. Results show that TWS-REC agrees well with observed total water storage (TWS-GRACE) in both HYZR (r = 0.94, NSE = 0.83) and HYER (r = 0.93, NSE = 0.83) over the period of 2003-2012. Estimated evaporation from both terrestrial water balance and atmospheric water balance method also agree well with each other in the HYZR (r = 0.89, NSE = 0.80) and in the HYER (r = 0.88, NSE = 0.79) over the period of 2000-2015. It suggests that reconstructed TWS and estimated evaporation are reliable for analyzing long-term water cycle in the study areas. Both the ratio of the estimated evaporation to precipitation (ER) in two basin increase first and then decreased during the study period. The correlation coefficients between ER and RR in the HYZR and HYER are -0.63 and -0.79, respectively, presenting that RR variability could be mainly caused by the evolution ER. Meanwhile it also indicates the nonignored role of total water storage (TWS) changes in RR variability in the two basin. TWS-REC in both regions have experienced significant increasing with rate of 26 mm/10a (HYZR, p < 0.05) and 17mm/10a (HYER, p < 0.05), later of which is the main reason of downward trend of RR in HYER. Further analysis indicates that changes in ER are resulted from comprehensive effects of precipitation variability (26.4mm/10a, p < 0.05 in HYZR and 3.5mm/10a p > 0.1 in HYER) and of dramatic climate warming (0.6℃/10a, p < 0.05 in HYZR and 0.5℃/10a, p < 0.05 in HYER). TWS changes in both basin are positively related with dramatic temperature rising and significant vegetation greening. It means that annual fluctuation of precipitation-runoff process (i.e., V-change RR) has affected negatively by climate warming and vegetation greening in the HYZR and HYER. These findings can advance our understanding of the runoff ratio evolution and water cycle in the headwater of Yangtze River and Yellow River and it is also important for ecological conservation strategy and downstream water resources management.</p>

The Mekong River is the dominant geo-hydrological structure in mainland Southeast Asia, originating in China and flowing through or bordering Myanmar, Laos, Thailand, Cambodia, and Vietnam. Whereas water resources in the wet season are more than adequate to fulfill basin needs, there are regional water shortages during the dry season, when only 1-2% of the annual flow reaches the Delta. Recent rapid agricultural and economic development in the basin has led to increasing competition among the riparian countries for Mekong waters. This development calls for a structured approach to the management of the basin, including efficient, equitable, and environmentally sustainable water allocation mechanisms that support the socioeconomic development in the region. Institutional mechanisms for Mekong cooperation among the riparians in the lower basin have been in place since 1957, and were revived in 1995. However, comprehensive water allocation mechanisms for the (lower) basin have not been developed to date. In this study, multi-country and intersectoral analyses of water allocation and use are carried out for the Mekong River Basin with the objective to determine tradeoffs and complementarities in water usage and strategies for the efficient allocation of water resources. An aggregate economic-hydrologic model for the basin is developed that allows for the analysis of water allocation and use under alternative policy scenarios. Results from the analytical framework indicate that although competition for Mekong water still appears to be very low, there are substantial tradeoffs between instream and off-stream water uses. An analysis of alternative water allocation mechanisms shows that to achieve both equitable and large benefits from water uses across countries and sectors, the ideal strategy would be to strive for optimal basin water use benefits and then to redistribute these benefits instead of the water resource. The development of such an integrated framework of analysis can be a critical first step to overcome some of the obstacles to effective management and joint cooperation in the Mekong River Basin. It could also facilitate the upcoming negotiations of water allocation rules in the lower basin and thus contribute to the reasonable and equitable utilization of Mekong River waters, as envisioned in the 1995 Mekong Agreement.

Rapid agricultural and economic development in mainland Southeast Asia during the 1990s has fueled the demand for water resources in the Mekong River Basin. An aggregate, integrated economic-hydrologic model for the basin is developed that allows for the analysis of water allocation and use under alternative policy scenarios. The model describes the water supply situation along the river system and the water demands by the various water-using sectors. Water benefit functions are developed for the major water uses subject to a series of physical and system control constraints. Water supply and demand are balanced based on the economic objective of maximizing net benefits to water use. Results from the analytical framework indicate that although competition for Mekong water still appears to be low, there are substantial tradeoffs between in-stream and off-stream water uses. Further development and refinement of such an integrated framework of analysis can be a critical step to overcome some of the obstacles to effective management and joint cooperation in the Mekong River Basin. It could also facilitate the ongoing negotiations of detailed water allocation rules in the lower basin and thus contribute to the reasonable and equitable utilization of Mekong River waters, as envisioned in the 1995 Mekong Agreement.

Life cycle analysis of urban water cycle in two Spanish areas: Inland city and island area

Managing water is a top social and economic responsibility and is expected to become even more critical as climate change, in addition to other human activities, alters water availability and quality. Robust indicators reflecting the effects of climate change on the US and global water cycles are needed in order to appropriately manage water resources. Here, we describe a suite of seventeen water cycle and management indicators, which are based on synthesis of available datasets. These indicators include average and heavy precipitation, standardized precipitation index, annual, 7-day low and 3-day high streamflow volume, streamflow timing, snow cover, snow water equivalent, groundwater level, lake water temperature, stream water temperature, dissolved oxygen, salinity, Palmer Drought Severity Index, water withdrawals, and water use. We also identify three indicators that could be included in the suite of water cycle and management indicators with some additional, directed work: snowfall, evapotranspiration, and soil moisture. Our conceptual framework focuses on known water cycle changes in addition to potential effects on management and addresses water quantity and quality, as well as water use and related interactions with freshwater ecosystems, societal impacts, and management. Water cycle indicators are organized into three categories: (1) hydrologic processes, (2) water quality processes, and (3) water quality and quantity impacts. Indicators described here are recommended to serve as critical references for periodic climate assessments. As such, these indicators support analyses of the effects of global change on the natural environment, agriculture, energy, and water resources, among other sectors. Additionally, we identify research gaps and needs that can be addressed to advance the development of future indicators.

Changes in the global water cycle critically impact environmental, agricultural, and energy systems relied upon by humanity (Jiménez Cisneros et al Climate Change 2014: Impacts, Adaptation, and Vulnerability (Cambridge: Cambridge University Press)). Understanding recent water cycle change is essential in constraining future projections. Warming-induced water cycle change is expected to amplify the pattern of sea surface salinity (Durack et al Science 336 455–8). A puzzle has, however, emerged. The surface salinity pattern has amplified by 5%–8% since the 1950s (Durack et al Science 336 455–8, Skliris et al Clim. Dyn. 43 709–36) while the water cycle is thought to have amplified at close to half that rate (Durack et al Science 336 455–8, Skliris et al Sci. Rep. 6 752). This discrepancy is also replicated in climate projections of the 21st century (Durack et al Science 336 455–8). Using targeted numerical ocean model experiments we find that, while surface water fluxes due to water cycle change and ice mass loss amplify the surface salinity pattern, ocean warming exerts a substantial influence. Warming increases near-surface stratification, inhibiting the decay of existing salinity contrasts and further amplifying surface salinity patterns. Observed ocean warming can explain approximately half of observed surface salinity pattern changes from 1957–2016 with ice mass loss playing a minor role. Water cycle change of 3.6% ± 2.1% per degree Celsius of surface air temperature change is sufficient to explain the remaining observed salinity pattern change.

Climate change and water resources: Case study of Eastern Monsoon Region of China

Agricultural production and wetland habitat quality in a coastal prairie ecosystem: simulated effects of alternative resource policies on land-use decisions

This paper introduces the Agriculture, Forestry and Fisheries Research Council of Japan (AFFRC) model, an integrated model that predicts future rice production in the Mekong River basin by taking into account the effect of global warming on both the water cycle and the rice economy. The model focuses especially on the water balance of paddy fields for different farmland water use systems. We defined six categories of irrigated paddies and three categories of rain-fed paddies on the basis of their systems of water usage. We included a process-based model to predict future rice production, accounting for daily changes in available water resources such as precipitation. Many models of crop production treat rice in the same way as other crops; the particular characteristics of rice farming are considered in more detail in our model. Our results show that it is possible to estimate future rice production in the Mekong River basin by taking into account changes in available water, and to model the resultant effects on the grain market.

A supply and demand model for rice in Cambodia, which includes among other factors evapotranspiration as a water supply variable impacting regional yields and planted areas, is developed to aid in the design of agricultural policies and planning. Impacts are determined stochastically by drawing on water cycle distributions and evaluating the resulting variation in production and price bands for local rice markets. The results of the baseline analyses indicate that production of wet and dry season rice steadily increases and the consumption per capita slightly decreases due to the negative income elasticity. Results of a partial stochastic analyses show that the production of rice in regions where elevations are high and the land vulnerable to flooding are the most sensitive to increased fluctuations in water supply. The changes also affect the rice market through equilibrium price changes. The upper price band, which is the width between average and 90th percentile, is larger than the lower band, which is the width between average and tenth percentile, suggesting that the situation of low income consumers could grow worse under an unstable environment with relatively larger upward price spikes. The results imply that development of irrigation facilities and water management systems maybe required for Cambodian provinces which rely heavily on agriculture, particularly rice production, under increasing climatic variation.

Triangle of Environment, Water and Energy: A Sociological Appraisal

Water cycle within the human civilization has become important with urbanization. To date, water cycle in the eco-system has been the focus in identifying the degree of water cycle in cities, but in practicality, water cycle within the human civilization system is taking on an increasing importance. While in recent years plans to reuse water have been implemented to restore water cycle in cities, the effect that such reuse has on the entire water cycle system has not been analyzed. The analysis on the effect that water reuse has on urban areas needs to be go beyond measuring the cost-savings and look at the changes brought about in the entire city's water cycle system. This study uses a SWAT model and water balance analysis to review the effects that water reuse has on changes occurring in the urban water cycle system by linking the water cycle within the eco-system with that within the human civilization system. The SWAT model to calculate the components of water cycle in the human civilization system showed that similar to measured data, the daily changes and accumulative data can be simulated. When the amount of water reuse increases in urban areas, the surface outflow, amount of sewer discharge and the discharged amount from sewage treatment plants decrease, leading to a change in water cycle within our human civilization system. The determinant coefficients for reduced surface outflow amount and reduced sewer discharge were 0.9164 and 0.9892, respectively, while the determinant coefficient for reduced discharge of sewage treatment plants was 0.9988. This indicates that with an increase in water reuse, surface flow, sewage and discharge from sewage treatment plants all saw a linear reduction.