Declining Groundwater Levels Research Articles

Sinkholes induced by uncontrolled groundwater withdrawal for agriculture in arid Saudi Arabia. Integration of remote-sensing and geophysical (ERT) techniques

Recently, an increasing number of sinkholes related to cavernous karst bedrock has been documented in the Kingdom of Saudi Arabia (KSA). One of the most hazardous areas is Al Jouf region, with an average annual rainfall below 35 mm. Here, crop fields irrigated with groundwater have experienced a very rapid expansion. Limited hydrogeological data indicate that the over-exploitation of the aquifers with very low recharge have caused a decline of around 50 m in the groundwater level. Landsat images acquired in 2002, 2015, and 2018 were utilized to automatically map and assess the expansion of agricultural activities in the area, as a proxy for groundwater withdrawal. The data indicate a rising expansion rate, from 57 km2/yr in the period 2002–2015, to 123 km2/yr during the 2015–2018 interval. The recent sinkhole spate is attributed to the growth of irrigated crops and the associated groundwater level decline, as supports the temporal and spatial correlation. It is proposed that the water level drawdown entails an increase in the effective weight of the roof of relict cavities formed in the past. This interpretation is substantiated at a specific sinkhole investigated by ERT. The geophysical investigation provides information of the position of the underlying cavity and indicates that its roof has been affected by buoyancy loss related to the anthropogenic water level decline.

Assessment of groundwater vulnerability to over-exploitation using MCDA, AHP, fuzzy logic and novel ensemble models: a case study of Goghat-I and II blocks of West Bengal, India

The vulnerability of groundwater to over-exploitation has been assessed in Goghat-I and II blocks of West Bengal using a number of different methods, i.e., MCDA, AHP, fuzzy logic and ensemble method in a GIS environment. Annual groundwater recharge has been measured through the water level fluctuation method, whereas groundwater abstraction data have been obtained from field investigations. The results of the assessment indicate that much of the study area is highly vulnerable to groundwater level decline due to excessive groundwater use. Result of all the methods reveals that very low and low vulnerable zones are present in north-eastern and southern parts in small extent. Extensive areas in the entire western, north-western and south-eastern parts represent high and very high vulnerable zones. Results of all the methods have been validated using the ROC curve, which produce AUC values of more than 0.8 for all the models. It shows that the applied methods produce reliable results. The methodologies developed in this study could be used to assess groundwater vulnerability to over-exploitation in other water-stressed regions.

Moroccan Groundwater Resources and Evolution with Global Climate Changes

In semi-arid areas, many ecosystems and activities depend essentially on water availability. In Morocco, the increase of water demands combined to climate change induced decrease of precipitation put a lot of pressure on groundwater. This paper reports the results of updating and evaluation of groundwater datasets with regards to climate scenarios and institutional choices. The continuous imbalance between groundwater extraction and recharge caused a dramatic decline in groundwater levels (20 to 65 m in the past 30 years). Additionally, Morocco suffers from the degradation in groundwater quality due to seawater intrusion, nitrate pollution and natural salinity changes. Climate data analysis and scenarios predict that temperatures will increase by 2 to 4 °C and precipitation will decrease by 53% in all catchments over this century. Consequently, surface water availability will drastically decrease, which will lead to more extensive use of groundwater. Without appropriate measures, this situation will jeopardize water security in Morocco. In this paper, we zoom on the case the Souss-Massa basin, where management plans (artificial recharge, seawater desalination, and wastewater reuse) have been adopted to restore groundwater imbalance or, at least, mitigate the recorded deficits. These plans may save water for future generations and sustain crop production.

Changes in the hydrological characteristics of Cauvery river draining the eastern side of southern Western Ghats, India

ABSTRACTThe changes in land use and regional climate together with human interventions affect the hydrological processes, resulting in the spatial and temporal alterations of surface and subsurface flow processes. Both climate and land surface change have adverse implications on the natural hydrological system in terms of variation in the run-off regime, surface storage, evapotranspiration, subsurface flow and infiltration, thereby affecting the hydrology of the river basin as a whole. Even though several studies worldwide have attempted to address the influence of climate change, land-use change and human activities on the hydrology of river basins, either as a whole or limited to a few components of the hydrological cycle, limited attention has been given to study the hydrological changes in the river basins of arid and semi-arid tropics, which are essentially fed by precipitation. The objective of the study is to analyse the changes in hydrological characteristics of the Cauvery river basin, a semi-arid river basin in South India. The changes in the hydrology of the Cauvery river basin are studied by analysing the trends in hydro-meteorological parameters using Mann-Kendall trend tests and Sen’s estimator of the slope. The results showed that the changes in the volume of rainfall and the number of rainy days significantly affect the overall hydrological regime of the river basin. The analysis of annual and seasonal rainfall over the Cauvery river basin showed a decreasing trend in the middle Cauvery basin. A declining trend in the number of rainfall events was also observed in the middle Cauvery region. The effect of decreasing trend in the volume of rainfall and number of rainy days is evident from the decreasing trends in the streamflow of the main channel and tributaries of the Cauvery river. The regions of increase in evapotranspiration showed a significant correlation with the regions which exhibited a decline in groundwater level.

Predicted Climate Change Impact on Groundwater Flow for the Upper Zone of Iraqi Aquifers

A 3D groundwater steady-state flow conceptual model was built for all of Iraq using a MODFLOW package integrated with the Groundwater Modeling System to simulate the groundwater movement and flow direction for the upper zone of Iraq as well as to compute the water budget for all aquifer systems in Iraq. This model was run for seven scenarios of climate change conditions for the period of 2020–2050. A Representative Concentration Pathway model (RCP4.5) was used for the prediction of future rainfall over the next 31 years. The results showed that the decline in rainfall will be 6.247% due to climate change impacts. The decline in rainfall will cover two-thirds of the area of Iraq. Seven scenarios simulating groundwater flow behavior showed that decreased soil moisture content will significantly reduce groundwater recharge and increase runoff. A decline in groundwater levels by an average of 1.8–4.8 m will occur for the upper zone of Iraqi aquifers over the next 31 years. These results will help Iraqi decision-makers improve water resource management.

Assessment of the potential areas for underground dam construction in Roomeshgan, Lorestan province, Iran

One of the methods for dealing with the problem of water shortage and the decline of groundwater levels in the arid areas is the construction of underground dams. It is difficult to make a decision about suitable locations for the construction of underground dams because of the necessity to consider numerous factors. Some of these criteria are hydrological, geological and geomorphologic characteristics of the area. By applying the GIS and AHP methods, this study attempted to introduce the suitable locations for construction of underground dams in Roomeshgan area in Lorestan Province, Iran. For this purpose, factors such as slope, lithology, land use, alluvium thickness, water quality, and distance from the well, fault and stream and rivers network were used. Using the Analytic Hierarchy Process (AHP) for the possibility of considering various qualitative and quantitative criteria, the process can be one way to select the appropriate location for constructing an underground dam. In this study, after the assessment of the used layers in the Expert Choice software, weight mapping of each layer was prepared. Then, the map of suitable areas for construction of the underground dam was prepared by overlapping the weight mappings of each layer in ArcGIS software. According to the results, 15.87 %, 11.96 %, 35.75 %, 33.23 % and 3.18 % of the region are located in very poor, poor, moderate, suitable and very suitable areas, respectively. After several field surveys of the area with three percent, six locations were selected for underground dam construction. The results show that the factors mentioned above have the most important role in locating the underground dam construction and the chosen method has high accuracy.

Determining Optimum Irrigation Termination Periods for Cotton Production in the Texas High Plains

HighlightsIrrigation water use efficiency was consistently higher under deficit irrigation as compared to full irrigation.Irrigation water use was always less than the annual allowable pumping limit under deficit irrigation.The first/second week of September was ideal for terminating irrigation under full/deficit irrigation in normal years.Ideal irrigation termination periods in wet/dry years were a week earlier/later than those in normal years.Abstract. Cotton ( L.) production in the Texas High Plains (THP) region relies heavily on irrigation with groundwater from the underlying Ogallala Aquifer. However, rapidly declining groundwater levels in the aquifer and increasing pumping costs pose challenges for sustainability of irrigated cotton production in this region. Adoption of efficient irrigation strategies, such as terminating irrigation at an appropriate time in the growing season, could enable producers to increase irrigation water use efficiency (IWUE) while maintaining desired yield goals. The objective of this study was to determine optimum irrigation termination periods for cotton production in the THP under full and deficit irrigation conditions using the Decision Support System for Agrotechnology Transfer (DSSAT) CROPGRO-Cotton model, which was evaluated in a prior study in the THP using measured data from an IWUE field experiment at Halfway, Texas. The treatment factors in the field experiment included irrigation capacities of 0 mm d-1 (low, L), 3.2 mm d-1 (medium, M), and 6.4 mm d-1 (high, H), applied during the vegetative, reproductive, and maturation growth stages. This study focused on a full irrigation (HHH) treatment and three deficit irrigation (LMH, LHM, and LMM) treatments. Eight irrigation termination dates with a one-week interval between 15 August and 30 September were simulated, and the impact of irrigation termination date on cotton IWUE and seed cotton yield were studied by dividing the 39-year (1978 to 2016) simulation period into dry, normal, and wet years based on the precipitation received from 1 April to the simulated irrigation termination date. Results indicated that the simulated IWUE was consistently higher under the LHM, LMH, and LMM treatments when compared to the HHH treatment. Based on the simulated average seed cotton yield and IWUE, optimum irrigation termination periods for cotton were found to be the first week of September (about 118 days after planting, DAP) for the HHH and LMH treatments and the second week of September (125 DAP) for the LHM and LMM treatments in normal years. In wet years, optimum irrigation termination periods were a week earlier than those in normal years and a week later in dry years for the HHH, LHM, and LMM treatments. For the LMH treatment, the optimum irrigation termination period in wet years was the same as that in normal years and two weeks later in dry years. The results from this study along with field-specific, late-season information will assist THP cotton producers in making appropriate irrigation termination decisions for improving economic productivity of the Ogallala Aquifer and thereby ensuring water security for agriculture. However, the recommendations from this study should be used with caution, as the optimum irrigation termination periods could potentially change with changes in cultivar characteristics, soil type, climate, and, crop management practices. Keywords: CROPGRO-Cotton, Deficit irrigation, DSSAT, Full irrigation, Irrigation water use efficiency, Seed cotton yield.

Assessment of land subsidence using interferometric synthetic aperture radar time series analysis and artificial neural network in a geospatial information system: case study of Rafsanjan Plain

Land subsidence resulting from groundwater extraction is a widely recurring phenomenon worldwide. To assess land subsidence, traditional methods such as numerical and finite element methods have limitations due to the complex interactions between the different constructor factors of aquifer in each area. We produced a groundwater-induced subsidence map by applying the geological and hydrogeological information of the aquifer system using an artificial neural network (ANN) combined with interferometric synthetic aperture radar (InSAR) and geospatial information system. The main problem with neural networks is providing the ground-truth dataset for training step. Therefore, the subsidence rate used as the network output was estimated using the InSAR time series analysis method. This study indicates the ANN approach is capable of knowing the mechanism of the land subsidence and can be used as a complementary of InSAR method to estimate the land subsidence with effective parameters and accessible data such as groundwater-level data especially in those areas in which measuring the subsidence was not feasible using InSAR. However, the results indicated that average groundwater depth and groundwater level decline were the most effective factors influencing subsidence in the study area using sensitivity analysis.

Impact of over-pumping on groundwater resources sustainability at Amman Zarqa basin, Jordan: a case study of arid areas affected by Syrian refugees crisis

Jordan is one of the most water-deprived countries worldwide. Groundwater is one of the main water resources in the country, nonetheless, long-term over-pumping, especially from the northern groundwater basin has been severely depleting the groundwater availability. This study evaluates the effects of over-pumping on groundwater quantity at the northeastern part of Amman Zarqa basin (Mafraq region including Zaatari Syrian Refugee Camp). Groundwater data were collected from the literature and the records of the Jordan Ministry of Water and Irrigation. Arcmap software was implemented to construct groundwater level, groundwater flow and aquifer thickness maps. The study area is mainly comprised of two groundwater aquifers, the Basaltic and the Amman Silicified Limestone aquifers. The outcomes of this evaluation indicate a severe decline in groundwater levels reaching up to a range of 1–5 m/year. This decline has led to a deterioration in the whole groundwater system and a noted reduction in the groundwater storage, reflected in the shrinkage of the aquifers’ saturated thicknesses.

GIS based probabilistic method in sinkhole susceptibility hazard zones

In this era of globalization, natural phenomena often invade the human population. Natural phenomena such as sinkholes often occur in countries whose topology lies in active limestone areas. Malaysia is one of the countries with active limestone areas, especially in the Klang Valley and its surrounding areas. Since 1968, the increase in sinkhole cases in Malaysia has been reported frequently. This has caused many building infrastructures to be destroyed, loss of life and destruction of property. So, one of the steps to overcome this problem is to do an in-depth study of the sinkhole. Therefore, Sinkhole Hazard Model (SHM) has been created with a combination of GIS integration by using probability techniques. There are five criteria suitable for Malaysian topography namely Lithology (LT), Soil Types (ST), Landuse (LU), Groundwater Level Decline (GLD) and Proximity to Groundwater Wells (PGW). Based on probability calculations, GLD and LU have shown a high impact on sinkhole formation. A hazard zonation map has been produced where it has been classified into five parts namely none, low, medium, high and very high. The results were validated with previous inventory data comprising 33 data. Based on the results obtained, 36.37% and 39.39% of the sinkhole formation has fallen into high and very high areas respectively. Based on these final results, the integration between GIS and probability techniques is useful in natural phenomena such as sinkhole formation.

Land Subsidence Vulnerability Assessment of Rural Settlements in Fars Province

Purpose- Land subsidence is caused by natural factors and human activities around the world. Fars Province, located in the south of Iran, is subject to land subsidence due to the uncontrolled exploitation of groundwater, causing damages to the population and human settlements and also environmental, social and economic areas. Design/methodology/approach- The present research is descriptive in terms of describing land subsidence in the case study region, whereas it is also analytical as time series analysis techniques based on Radar Interferometry (InSAR) is applied to monitor temporal changes in subsidence in Darab and Fasa Plains, including 470 rural points. Using 8 ENVISAT ASAR images spanning between 2005 and 2010, nine Interferograms were processed. In the study area. Geographic Information System (GIS) is then used to study groundwater level decline at the well locations in a 24-year period (from 1991 to 2015). Findings- The results of the research confirm that there is a significant correlation between groundwater water level decline and land surface subsidence. Time series analysis of the processed Interferograms indicate the mean displacement velocity map, demonstrating the maximum subsidence rate of 25 cm/yr. The InSAR analysis reveal within the study area subsidence rate of 25 cm/year in 24 years period and locally exceeding 30 cm/yr in the last decade. This area of significant subsidence is limited in its spatial extent to the agricultural land and is partly influenced by the large-scale over-exploitation of groundwater resources in the region study. The temporal and areal relationships of subsidence and groundwater level data suggest that a significant part of the observed subsidence in the Darab region is caused by intense groundwater extraction which has led to widespread compaction within the upper parts of the up to 300m. Socioeconomic analysis and the subsidence hazard map show that 105523 people are generally at risk of subsidence, of 65068 who are at high risk. In addition, there are 2679 socioeconomic infrastructures such as public service at risk of damage by land subsidence. Research limitations/implications- Limitation in In SAR data access, especially for long-term data was one of the main limitations in land subsidence research and also in this research. Practical implications- Integrated water resource management and the observed extraction of groundwater could influence the subsidence rate in the regions exposed to land subsidence. Originality/value- This research will be important to provide vulnerability in regions with groundwater overexploitation.

Groundwater Policy and Ground Water Dependencies: Reflecting on the Evolving Socio-Environmental Dynamics in Peri-Urban Kathmandu Valley

Groundwater is an increasingly important source of water supply in Kathmandu Valley, ‘the hub of Nepal’s urbanisation’. Past studies have revealed that groundwater extraction in Kathmandu Valley exceeds its recharge, thus having negative consequences like drying of traditional water sources, decreasing yield of wells, and declining groundwater levels. The groundwater policy 2012 was formulated with the aim of managing groundwater use in the valley. Yet, with rapid urban growth, groundwater exploitation has continued increasing in the city and the peri-urban areas in Kathmandu Valley. But little is known regarding how urbanisation shapes increasing groundwater exploitation in the peri-urban settings. This study unfolds the underexplored socio-environmental dynamics underlying groundwater exploitation in peri-urban areas of Kathmandu Valley. The findings from the case study using qualitative research methods, conducted in peri-urban locations of Kathmandu Valley show increasing competition for water and growing use of as well as dependence on groundwater in these rapidly evolving peri-urban spaces, despite growing protests and worries about its consequences. However, the existing groundwater policy lacks attention to peri-urban dynamics of change and growth and does little to address the increasing groundwater use in peri-urban locations in the valley. The polarised views and local conflicts around groundwater exploitation emerging in peri-urban spaces are the outcome of multiple entanglements: sectoral divides and overlapping responsibilities in water institutions, weak governance and management; socio-economic transformations in peri-urban spaces, the invisibility of groundwater and ambiguity in the hydrological dynamics of conjunctive water use. Based on my findings, I stress on the need for addressing the existing macro-micro gaps (ground)water management by improving the understanding of local hydro-geological complexities and paying critical attention to the socio-economic, political and institutional drivers of increasing groundwater use.

The Economic Value of Irrigation Water in Wadi Zabid, Tihama Plain, Yemen

This study used crop budgets to assess the impact of declining groundwater levels on the economic value of irrigation water in the Wadi Zabid region of Yemen. The study found that returns to land and water were highly sensitive to changes in groundwater depths over time and the free availability of spate water for irrigation. Crops differed in the amounts of irrigation water applied and in their returns to land and water. Banana had the highest irrigation requirement, but also delivered the highest return to land. Banana’s return to water was greater than that of date palm and feed sorghum, but lower than that of mango and food sorghum.

Regional scale trend and variability of rainfall pattern over agro-climatic zones in the mid-Mahanadi river basin of eastern India

Investigation of trends and variability in rainfall patterns is of paramount importance for the effective planning and management of rainfed cropping systems. In this study, a detailed analysis is carried out to understand the changes in rainfall patterns and characteristics at a regional scale on agro-climatic zone basis, in the mid-Mahanadi river basin. Daily rainfall data of India Meteorological Department (IMD) at 0.25° × 0.25° spatial resolution has been analyzed for the period of 1979–2013 on a monthly, seasonal, and annual timescale to investigate variability, trends, and seasonality of rainfall. Results of analysis reveal that there is large spatio-temporal variation in the river basin with a shift in seasonality of rainfall, with increased prolonged dry spells, and significant increase in extreme weather events over the agro-climatic zones (AZ). Most of the agro-climatic zones are found to have significant decreasing trends in the magnitude of rainfall during the non-monsoon season. In particular, agro-climatic zones nearer to the coastal region are more vulnerable to the high rainfall, whereas the North-Eastern-Ghat (AZ67) and Western-Central-Table (AZ68) regions are susceptible to the moisture stress. Further, analysis of groundwater level fluctuation shows a significant decline in groundwater level during the monsoon as well as non-monsoon seasons. The resulted effect of rainfall variability can be seen in terms of an increase in the prolonged dry spells as well as decline in the groundwater level. Moreover, the results of this study indicate a climate change signal at the regional scale that will help the policymakers and water managers to identify the critical agro-climatic zones in the mid-Mahanadi river basin for the formulation of efficient water resources management and planning strategies, particularly for the major crops of the rainfed agriculture regions.

Groundwater use and rapid irrigation expansion in a changing climate: Hydrological drivers in one of the world’s food bowls

In recent decades, increased groundwater use enabled a large areal increase in irrigated dry season crops in northwest Bangladesh. Concurrent declining groundwater levels across the region are of great concern for food security. A water balance model approach that considered changes in irrigated agriculture was implemented to assess changes over the long-term to three five-year evaluation periods (1985–1989, 1998–2002 and 2011–2015) and seasonally (annual, dry season and wet season). The model used two different methods that explicitly capture changes in irrigation to compute and compare actual evapotranspiration (ETa). The first method used MODIS satellite data to estimate a crop coefficient based on vegetation indices (at 500 m spatial resolution) scaled by reference crop evapotranspiration (ETref). The second method used a crop coefficient approach based on survey data of crop areas at the district level and subsequently scaled by ETref. Both methods yielded very similar results at the district level, with correlation coefficients between 0.75 and 0.89. The maximum difference between the monthly averages was only of 5.4%. Notwithstanding the observed overall increase in irrigated areas, estimated overall mean annual ETa is similar through the analysis (ca. 1100 mm) and district-level trends were mixed (some increasing and some decreasing) showing in some districts a weak association between ETa and the related declining groundwater level. From the water balance, it is inferred that both the groundwater extraction (by pumping for irrigation and capillary rise to supply roots) and the groundwater recharge reduced from 1998–2002 to 2011–2015, and with deeper groundwater in later years, much of the irrigation water supply is by soil water storage rather than by groundwater. As highlighted in this paper, there are other factors aside crop expansion that may have contributed to the groundwater decline, thus a single policy or management change such as restricting groundwater extraction for irrigation may alone be inadequate to reverse declining groundwater trends.

Groundwater Governance Reforms: A Possible Licensing Framework for Groundwater Abstraction and Use

Over the past decades, incidents of extensive groundwater level decline, contamination of groundwater aquifers and extraction of poor quality water have become more intense. Both over exploitation and pollution of groundwater systems are largely a result of human activities on the surface. These may include agriculture, domestic and public use, industrial use, energy etc. All these economy sectors are inherently linked: they all vitally depend on groundwater but at the same time represent the most immediate threats to its sustainable management and conservation. That being the case, it is apparent that any governance system for the management and conservation of this valuable resource must walk a fine line in balancing competing or conflicting interests among stakeholders, and coordinating with urban and rural land uses and the management of the entire subsurface space.Against this background, the present paper critically explores possible types of groundwater governance reforms and provides an example of what a successful national framework for sustainable qualitative and quantitative groundwater abstraction and use might look like.

Modeling Water and Nitrogen Balance of Different Cropping Systems in the North China Plain

The North China Plain (NCP) is experiencing serious groundwater level decline and groundwater nitrate contamination due to excessive water pumping and application of nitrogen (N) fertilizer. In this study, grain yield, water and N use efficiencies under different cropping systems including two harvests in 1 year (winter wheat–summer maize) based on farmer (2H1Y)FP and optimized practices (2H1Y)OPT, three harvests in 2 years (winter wheat–summer maize–spring maize, 3H2Y), and one harvest in 1 year (spring maize, 1H1Y) were evaluated using the water-heat-carbon-nitrogen simulator (WHCNS) model. The 2H1YFP system was maintained with 100% irrigation and fertilizer, while crop water requirement and N demand for other cropping systems were optimized and managed by soil testing. In addition, a scenario analysis was also performed under the interaction of linearly increasing and decreasing N rates, and irrigation levels. Results showed that the model performed well with simulated soil water content, soil N concentration, leaf area index, dry matter, and grain yield. Statistically acceptable ranges of root mean square error, Nash–Sutcliffe model efficiency, index of agreement values close to 1, and strong correlation coefficients existed between simulated and observed values. We concluded that replacing the prevalent 2H1YFP with 1H1Y would be ecofriendly at the cost of some grain yield decline. This cropping system had the highest average water use (2.1 kg m−3) and N use efficiencies (4.8 kg kg–1) on reduced water (56.64%) and N (81.36%) inputs than 2H1YFP. Whereas 3H2Y showed insignificant results in terms of grain yield, and 2H1YFP was unsustainable. The 2H1YFP system consumed a total of 745 mm irrigation and 1100 kg N ha–1 in two years. When farming practices were optimized for two harvests in 1 year system (2H1Y)OPT, then grain yield improved and water (18.12%) plus N (61.82%) consumptions were minimized. There was an ample amount of N saved, but water conservation was still unsatisfactory. However, considering the results of scenario analyses, it is recommended that winter wheat would be cultivated at <200 mm irrigation by reducing one irrigation event.

Change in regional land subsidence in Beijing after south-to-north water diversion project observed using satellite radar interferometry

ABSTRACTOver-exploitation of groundwater has caused severe land subsidence in Beijing during the past two decades. Since the middle route of South-to-North Water Diversion Project (SNWDP), the biggest water diversion project in China, started to deliver water to Beijing in December 2014, the groundwater shortage has been greatly alleviated. This study aims to analyze the impact of SNWDP on the spatiotemporal evolution of land subsidence in Beijing. Change in surface displacement in Beijing after SNWDP was retrieved and the spatiotemporal patterns of the change were analyzed based on long time-series Envisat Advanced Synthetic Aperture Radar (ASAR) (2004–2010), Radarsat-2 (2011–2014), and Sentinel-1 (2015–2017) satellite datasets using Permanent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) techniques. Land subsidence unevenness index (LSUI) was proposed to represent the spatial unevenness of surface displacement. PS-Time approach was then adapted to examine the time series evolution of LSUI. The results showed that the InSAR measurements agree well with leveling measurements with R2 over 0.96. Although the maximum annual displacement rate reached −159.7 mm/year by 2017, over 57% of the area within 25 mm/year contour line showed decreasing or unchanged displacement rate after the south-north water delivered to Beijing. The settlement rate in Chaoyang-Dongbalizhuang (CD) subsidence center has decreased for 26 mm/year from 2011–2014 to 2015–2017. Only around 15% of the area experienced continued accelerating settlement rate through the three time periods, which was mainly located in the area with the compressible layer thickness over 190 m, while the magnitude of velocity increment considerably decreased after SNWDP. Land subsidence unevenness, represented by LSUI, developed more slowly after SNWDP than that during 2011–2014. However, LSUI at the edge of settlement funnel has kept developing and reached 1.7‰ in 2017. Decreasing groundwater level decline after SNWDP and the positive relationship (R2 > 0.74) between land subsidence and groundwater level clearly showed impacts of SNWDP on the alleviating land subsidence. Other reasons include geological background, increasing precipitation, and strict water management policies implemented during these years.

Comparison of water-use patterns for non-native and native woody species in a semiarid sandy region of Northeast China based on stable isotopes

In the semiarid sandy region of Northeast China, non-native woody species such as Pinus sylvestris var. mongolica L. and Populus x xiaozhuanica W.Y. Hsu & Liang frequently suffer dieback during years of extreme drought events due to water deficiency. In contrast, dieback does not usually occur in native woody species, e.g., Pinus tabuliformis Carr., Ulmus pumila L., and shrub Caragana microphylla Lam. However, the mechanism of water-use patterns between the non-native and native woody species remain unclear, which limits our understanding of the mechanisms underlying dieback of non-native woody species. During two consecutive growing seasons in 2014 and 2015, sources of water uptake by two non-native (P. mongolica and P. xiaozhuanica) and three native (P. tabuliformis, U. pumila and C. microphylla) woody species were determined using the stable isotopes of δ2H and δ18O in the twig xylem water, soil water at various depths (0–200 cm), groundwater (water from capillary fringe or beneath the water table) and precipitation, coupled with soil moisture and groundwater level measurements. Results showed that both P. mongolica and P. tabuliformis trees used the 0–100 cm soil water in the spring and the 0–40 cm and 0–100 cm soil water in summer of 2014 and autumn of 2015, respectively, when soil moisture was high. In contrast, in summer of 2015 and autumn of 2014, when soil moisture was low, P. mongolica trees used both the 0–100 cm soil water and groundwater, whereas P. tabuliformis trees used the 0–200 cm soil water and both the 40–200 cm soil water and relatively limited groundwater, respectively. The P. xiaozhuanica trees used the 40–200 cm or the 100–200 cm soil water and groundwater, whereas U. pumila trees mainly used the 0–100 cm or 0–200 cm soil water, except in autumn when soil moisture was high. P. xiaozhuanica trees used the 0–200 cm soil water, while U. pumila trees used the 0–40 cm soil water. The shrub C. microphylla mainly used the 0–200 cm soil water during the measurement period irrespective of soil moisture conditions. Compared with the native woody species, which mainly used soil water, the non-native tree species relied on groundwater besides soil water, especially under low soil moisture conditions. Therefore, a sharp decline in groundwater level during extreme drought years might have a strong negative impact on the growth and survival of non-native woody species.

Detecting Winter Wheat Irrigation Signals Using SMAP Gridded Soil Moisture Data

The southern part of the Hebei Province is one of China’s major crop-producing regions. Due to the continuous decline in groundwater level, agricultural water use is facing significant challenges. Precision agricultural irrigation management is undoubtedly an effective way to solve this problem. Based on multisource data (time series soil moisture active passive (SMAP) data, Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) and evapotranspiration (ET), and meteorological station precipitation), the irrigation signal (frequency, timing and area) is detected in the southern part of the Hebei Province. The SMAP data was processed by the 5-point moving average method to reduce the error caused by the uncertainty of the microwave data derived SM. Irrigation signals can be detected by removing the precipitation effect and setting the SM change threshold. Based on the validation results, the overall accuracy of the irrigation signal detection is 77.08%. Simultaneously, considering the spatial resolution limitation of SMAP pixels, the SMAP irrigation area was downscaled using the winter wheat area extracted from MODIS NDVI. The analytical results of 55 winter wheat samples (5 samples in a group) showed that winter wheat covered by one SMAP pixel had an 82.72% growth consistency in surface water irrigation period, which can indicate a downscaling effectiveness. According to the above statistical analysis, this paper considers that although the spatial resolution of SMAP data is insufficient, it can reflect the change of SM more sensitively. In areas where the crop pattern is relatively uniform, the introduction of high-resolution crop pattern distribution can be used not only to detect irrigation signals but also to validate the effectiveness of irrigation signal detection by analyzing crop growth consistency. Therefore, the downscaling results can indicate the true winter wheat irrigation timing, area and frequency in the study area.