Water sustainability and watershed ecosystem health (Editorial)

Climate change and human activities have unprecedentedly altered the hydrological processes and ecosystem services of watersheds all over the world, causing or exacerbating local and regional water crises, threatening ecosystem integrity, and compromising water sustainability. Understanding the effects of interactions and dynamics of such coupled human and natural systems on eco-hydrological processes at the watershed scale is essential for addressing and adapting to global environmental chang

Multi-Scale Evaluation of the SMAP Product Using Sparse In-Situ Network over a High Mountainous Watershed, Northwest China

As the latest L-band mission to date, evaluation of the Soil Moisture Active Passive (SMAP) products is one of its post-launch objectives. However, almost all previous studies have been conducted at the core validation sites (CVS) of the SMAP mission. This paper presents an evaluation of the SMAP soil moisture Level 3 (L3) and Level 4 (L4) products under different vegetation types at multiple tempo-spatial scales over the upper reach of the Heihe River Watershed, a topographically complex mountainous area in Northwest China. This was done through comparisons of the L3 and L4 products with ground-based observations from a sparse in situ network of permanent and temporary stations from 1 April 2015 to 22 June 2017. Results show that, compared with in situ observations at point scale, both the L3 and L4 products represent the temporal trends of the in situ observations in the study area well, with R values of 0.601 and 0.538 for the L3 ascending and descending products, respectively, and ranging from 0.353 to 0.410 for the L4 product at eight overpassing moments. However, because of the uncertainties of brightness temperature TBp and effective temperature Teff as well as their propagations in the inversion algorithm, both products did not achieve the accuracy of 0.04 m3/m3 in mountainous area. These uncertainties also result in the “dry bias” of the SMAP products in almost all the evaluations to date. Compared with areal average values at the watershed scale, the L3 product is far beyond the accuracy of 0.04 m3/m3 and the L4 product basically achieves the accuracy. In vegetation-covered land, the suitability and the variability of the coefficient bp result in both products performing best in cropland, then coniferous forest, sparse grassland, dense grassland, and alpine meadow, and worst in shrub. In barren land, the errors in estimating surface roughness h caused by the complex topography lead to poor performance of the SMAP products. With the relative errors of the SMAP brightness temperature observations and the corresponding land model forecast in the assimilation; the L3 and L4 products show different performance at both temporal and spatial scales; and the L3 product provides more reliable soil moisture estimates in the study area. Based on the results of this study, we propose: quantifying the uncertainties in estimating brightness temperature TBp and effective temperature Teff; determine coefficient bp and surface roughness h factor under various conditions; improving Goddard Earth Observing Model System Version 5 (GEOS-5) model; and deriving the SMAP-only climatology to improve the SMAP soil moisture estimates in the future

Analysis of Agricultural Land Use Change in the Middle Reach of the Heihe River Basin, Northwest China

The Heihe River Basin (HRB) is the second largest inland river basin in arid Northwest China. The expanding agricultural irrigation, growing industrialization, and increasing urban development in the middle reach have depleted much of the river flow to the lower reach, degrading the corresponding ecosystems. Since the enactment of the State Council of China’s new HRB water allocation policy in 2000 tremendous land use and land cover (LULC) changes have taken place to reduce water consumption in the middle reach and deliver more water downstream. This paper analyzes LULC changes during the period of 2000–2009 to understand how the changing land use patterns have altered water resource dynamics in the region. Results, while yet to be further verified in the field, show that from 2000 to 2009, urban, agricultural land, rangeland, and forest areas have increased, and barren area has decreased. Within the cropland, rice (a high water consumption crop) planting area decreased, while corn and wheat (relatively lower water consumption crops) planting areas increased. These changes in land use patterns, especially in the agricultural zones, have ensured the discharge of the required amount of water to the lower reach

Human settlement and changes in the distribution of river systems in the Minqin Basin over the past 2000 years in Northwest China

Introduction: Arid area is an important base for human settlement, however, long and drastic human activities have altered the drainage patterns in the arid watersheds significantly, causing serious ecological consequences. This study, through a case study of the Minqin Basin, a microcosm of the artificial oases in the arid northwest China, used the multi-types of data to recover the spatial distribution of human settlement and drainage patterns during historical period and analyze the relationship between them over the past 2000 years. Outcomes: Before the Han Dynasty (121 BC), the utilization of water resources in the Minqin Basin was in the primitive stage and the drainage pattern maintained the natural state. From the Han (121 BC- 220) to the Wei-Jin Dynasties (220- 316), the utilization of water resources intensified unprecedentedly, but the natural shape of the river systems was still maintained. In the following 1,000 years or so, the drainage pattern was in the state of “following its own course” due to the small human population. In the Ming Dynasty (1368-1644), with the alteration of the main rivers, the water resource utilization increased obviously, but the human reclamations were mainly confined to the southern part of the basin. In the Qing Dynasty (1644-1911), the reclamation of the Liulin Lake area significantly changed the drainage patterns, resulted in the drastically northward expansion of human settlement. Since the foundation of the People’s Republic of China (PRC) in 1949, the artificial water system completely replaced the natural water system and intensified the ecological problems in the basin. Discussion: The changes over the past 2000 years show the drastic impacts of human activities on the alterations of the drainage patterns and related ecological problems in the arid Northwest China. Conclusion: Rehabilitation of such ecological impairments requires both ecological restoration projects and changes in human paradigm and behavior over multiple temporal and spatial scales