scholarly journals A Review of Earth Observation-Based Analyses for Major River Basins

2019 ◽  
Vol 11 (24) ◽  
pp. 2951 ◽  
Author(s):  
Soner Uereyen ◽  
Claudia Kuenzer
Keyword(s):  
Land Surface ◽  
Spatial Databases ◽  
Spatial Information ◽  
Environmental Changes ◽  
River Basins ◽  
Global Scale ◽  
Earth Observation ◽  
Basin Scale ◽  
The Status ◽  
Major River

Regardless of political boundaries, river basins are a functional unit of the Earth’s land surface and provide an abundance of resources for the environment and humans. They supply livelihoods supported by the typical characteristics of large river basins, such as the provision of freshwater, irrigation water, and transport opportunities. At the same time, they are impacted i.e., by human-induced environmental changes, boundary conflicts, and upstream–downstream inequalities. In the framework of water resource management, monitoring of river basins is therefore of high importance, in particular for researchers, stake-holders and decision-makers. However, land surface and surface water properties of many major river basins remain largely unmonitored at basin scale. Several inventories exist, yet consistent spatial databases describing the status of major river basins at global scale are lacking. Here, Earth observation (EO) is a potential source of spatial information providing large-scale data on the status of land surface properties. This review provides a comprehensive overview of existing research articles analyzing major river basins primarily using EO. Furthermore, this review proposes to exploit EO data together with relevant open global-scale geodata to establish a database and to enable consistent spatial analyses and evaluate past and current states of major river basins.

scholarly journals Evaluating the hydrological consistency of satellite based water cycle components

2016 ◽  
Author(s):  
Oliver López ◽  
Rasmus Houborg ◽  
Matthew F. McCabe
Keyword(s):  
Land Surface ◽  
Water Budget ◽  
Large Scale ◽  
Water Cycle ◽  
Satellite Observation ◽  
Global Scale ◽  
Satellite Observations ◽  
Arid Environments ◽  
Basin Scale ◽  
Wide Range

Abstract. Advances in multi-satellite based observations of the earth system have provided the capacity to retrieve information across a wide-range of land surface hydrological components and provided an opportunity to characterize terrestrial processes from a completely new perspective. Given the spatial advantage that space-based observations offer, several regional-to-global scale products have been developed, offering insights into the multi-scale behaviour and variability of hydrological states and fluxes. However, one of the key challenges in the use of satellite-based products is characterizing the degree to which they provide realistic and representative estimates of the underlying retrieval: that is, how accurate are the hydrological components derived from satellite observations? The challenge is intrinsically linked to issues of scale, since the availability of high-quality in-situ data is limited, and even where it does exist, is generally not commensurate to the resolution of the satellite observation. Basin-scale studies have shown considerable variability in achieving water budget closure with any degree of accuracy using satellite estimates of the water cycle. In order to assess the suitability of this type of approach for evaluating hydrological observations, it makes sense to first test it over environments with restricted hydrological inputs, before applying it to more hydrological complex basins. Here we explore the concept of hydrological consistency, i.e. the physical considerations that the water budget impose on the hydrologic fluxes and states to be temporally and spatially linked, to evaluate the reproduction of a set of large-scale evaporation (E) products by using a combination of satellite rainfall (P) and Gravity Recovery and Climate Experiment (GRACE) observations of storage change, focusing on arid and semi-arid environments, where the hydrological flows can be more realistically described. Our results indicate no persistent hydrological consistency in these environments, suggesting the need for continued efforts in improving satellite observations, particularly for the retrieval of evaporation, and the need to more directly account for anthropogenic influences such as agricultural irrigation into our large scale water cycle studies.

scholarly journals Hydrological recurrence as a measure for large river basin classification and process understanding

2014 ◽  
Vol 11 (7) ◽  
pp. 8191-8238 ◽  
Author(s):  
R. Fernandez ◽  
T. Sayama
Keyword(s):  
River Basin ◽  
Land Surface ◽  
Fourier Transforms ◽  
Land Surface Model ◽  
Arctic Region ◽  
River Basins ◽  
Large River ◽  
Global Scale ◽  
Surface Model ◽  
Monsoon Area

Abstract. Hydrologic functions of river basins are summarized as water collection, storage and discharge, which can be characterized by the dynamics of hydrological variables including precipitation, evaporation, storage and runoff. In some situations these four variables behave more in a recurrent manner by repeating in a similar range year after year or in other situations they exhibit more randomness with higher variations year by year. The degree of recurrence in runoff is important not only for water resources management but also for hydrologic process understandings, especially in terms of how the other three variables determine the degree of recurrence in runoff. The main objective of this paper is to propose a simple hydrologic classification framework applicable to global scale and large basins based on the combinations of recurrence in the four variables. We evaluate it by Lagged Autocorrelation, Fast Fourier Transforms and Colwell's Indices of variables obtained from EU-WATCH dataset composed by eight hydrologic and land surface model outputs. By setting a threshold to define high or low recurrence in the four variables, we classify each river basin into 16 possible classes. The overview of recurrence patterns at global scale suggested that precipitation is recurrent mainly in the humid tropics, Asian Monsoon area and part of higher latitudes with oceanic influence. Recurrence in evaporation was mainly dependent on the seasonality of energy availability, typically high in the tropics, temperate and subarctic regions. Recurrence in storage at higher latitudes depends on energy/water balances and snow, while that in runoff is mostly affected by the different combinations of these three variables. According to the river basin classification 10 out of the 16 possible classes were present in the 35 largest river basins in the world. In humid tropic region, the basins belong to a class with high recurrence in all the variables, while in subtropical region many of the river basins have low recurrence. In temperate region, the energy limited or water limited in summer characterizes the recurrence in storage, but runoff exhibits generally low recurrence due to the low recurrence in precipitation. In the subarctic and arctic region, the amount of snow also influences the classes; more snow yields higher recurrence in storage and runoff. Our proposed framework follows a simple methodology that can aid in grouping river basins with similar characteristics of water, energy and storage cycles. The framework is applicable at different scales with different datasets to provide useful insights into the understanding of hydrologic regimes based on the classification.

A New Global Assessment of the Status and Trends of Desertification

1984 ◽  
Vol 11 (2) ◽  
pp. 103-113 ◽  
Author(s):  
Jack A. Mabbutt
Keyword(s):  
Land Surface ◽  
Regional Scale ◽  
State Level ◽  
Global Scale ◽  
Population Estimates ◽  
Developing Regions ◽  
Critical Areas ◽  
The Earth ◽  
Status And Trends ◽  
The Status

A reassessment of the status and trends of desertification was called for as part of a general assessment of progress in the implementation of the United Nations Plan of Action to Combat Desertification, seven years after the UN Conference on Desertification (UNCOD) in 1977. Because of the inadequate data existing at the country or state level, the basic generalization has been set at a wider regional scale. The new assessment has confirmed the global scale of the problem of desertification as presented to UNCOD, and has increased the area and populations considered to be at risk through its recognition of the threat of desertification in the sub-humid tropics. The threatened area of 4,500 million ha constitutes 35% of the land surface of the Earth, with almost 20% (850 millions) of the world's total human population. Estimates indicate that, of this area, 75% is already moderately desertified, and 30% is severely or very severely desertified.The rural population affected by severe desertification totals some 280 millions, or 470 millions if the urban component is included, with, respectively, 135 millions and 190 millions severely affected. These are significantly larger than the figures presented to UNCOD—mainly through the inclusion of additional sub-humid land in this assessment, but partly through national population increases and growth in the extent of severely desertified land. Both in terms of areas and population affected, the so-called developing regions are shown to be those worst-hit by desertification; and within these, the tropical semiarid and sub-humid lands tend to be the most ‘critical’ areas.

Synergetic analyses of Earth observation time series on land surface dynamics in large river basins

2021 ◽  
Author(s):  
Soner Uereyen ◽  
Felix Bachofer ◽  
Juliane Huth ◽  
Claudia Kuenzer
Keyword(s):  
Time Series ◽  
River Basin ◽  
Land Surface ◽  
Partial Correlation ◽  
River Basins ◽  
Earth Observation ◽  
Anthropogenic Pressure ◽  
Western Himalayas ◽  
Surface Dynamics ◽  
Snow Cover Extent

<p>Long-term Earth observation (EO) time series are an inevitable source for past quantification and analysis as well as future forecasting of land surface dynamics. This study investigates the joint use of geoscientific time series over the last two decades, including EO-based MODIS vegetation indices, DLR Global WaterPack, DLR Global SnowPack, and DLR World Settlement Footprint as well as further climate and hydrological variables to quantify and evaluate land surface changes and their potential drivers.</p><p>For this purpose, we focus on the Indus-Ganges-Brahmaputra-Meghna (IGBM) river basin in South Asia, being the most populated and one of the most diverse river basins worldwide. In detail, it is characterized by multiple climate zones, including arid climate in the west, polar climate in the north, and tropical climate in the south east. Moreover, the northern areas of these river basins are shaped by the Himalayan mountain range, also known as the water tower of Asia, whereas the downstream areas are characterized by fertile soils and intensive agriculture in the Indo-Gangetic Plain, being dominated by extreme rainfalls during southwest summer monsoon. Here, the availability of water is of paramount importance in social, economic, as well as political terms, but threatened by climate change as well as anthropogenic pressure.</p><p>To enhance the understanding of land surface processes in the IGBM river basin, we apply state-of-the-art time series analysis techniques, including quantification and evaluation of trends and changepoints. Furthermore, we use partial correlation and a causal discovery approach to explore driving factors of land surface change. Changes and patterns are investigated with respect to the prevailing seasons over the study area. Methods were implemented with focus on spatial and temporal transferability to enable further large-scale analysis in the future. Initial results covering the last two decades over the IGBM river basin indicate an increase in greening of vegetation, mostly in areas dominated by croplands. Considering snow cover extent, we observed a decline over the Eastern Himalayas and an increase over the Western Himalayas. Moreover, changes of surface water extent are mixed over the river basin, with negative trends along the Brahmaputra and Ganges rivers and positive trends close to the Bay of Bengal. In addition, preliminary results considering linkages between EO and climate variables reveal strong partial correlation between vegetation and precipitation in western areas, whereas temperature is the dominating climate factor over eastern areas of the IGBM river basin.</p>

An Environmental History of Southern Africa

2020 ◽  
Author(s):  
Jasper Knight
Keyword(s):  
Environmental History ◽  
Southern Africa ◽  
Land Surface ◽  
Environmental Changes ◽  
Late Quaternary ◽  
Global Scale ◽  
Time Intervals ◽  
Ecological Processes ◽  
Environmental Controls ◽  
Proxy Indicators

Southern Africa has experienced significant environmental changes since the breakup of the Gondwana supercontinent, starting around 180 million years ago. These environmental changes broadly reflect the interplay between tectonic and global-scale climatic drivers, which in combination result in changes to the properties and dynamics of land surface physical and ecological processes. The preserved record of such processes can be used as proxy indicators to reconstruct past environments and climates. In southern Africa, different types of proxy indicators have formed and are preserved in different geographical areas, broadly corresponding to their individual climatic and geomorphic contexts. Three significant time intervals over which landscape evolution have taken place are the Phanerozoic, the late Quaternary, and the last 200 years. A critical outcome of this analysis is that the record of environmental change in southern Africa is highly variable and only partly preserved, and that there are spatial and temporal gaps which mean that it is difficult to construct a continuous or unambiguous environmental history either for all areas of the region or for all time intervals. Changing physical drivers and environmental controls over time, including land surface feedbacks, are now being supplanted by a stronger imprint of human activity in the Anthropocene.

scholarly journals Satellite-Based Evapotranspiration in Hydrological Model Calibration

2020 ◽  
Vol 12 (3) ◽  
pp. 428 ◽  
Author(s):  
Lulu Jiang ◽  
Huan Wu ◽  
Jing Tao ◽  
John S. Kimball ◽  
Lorenzo Alfieri ◽  
...  
Keyword(s):  
Land Surface ◽  
Model Calibration ◽  
Hydrological Model ◽  
Land Surface Model ◽  
River Basins ◽  
Global Scale ◽  
Surface Model ◽  
Model Parameters ◽  
Spatially Distributed ◽  
Streamflow Simulation

Hydrological models are usually calibrated against observed streamflow (Qobs), which is not applicable for ungauged river basins. A few studies have exploited remotely sensed evapotranspiration (ETRS) for model calibration but their effectiveness on streamflow simulation remains uncertain. This paper investigates the use of ETRS in the hydrological calibration of a widely used land surface model coupled with a source–sink routing scheme and global optimization algorithm for 28 natural river basins. A baseline simulation is a setup based on the latest model developments and inputs. Sensitive parameters are determined for Qobs and ETRS-based model calibrations, respectively, through comprehensive sensitivity tests. The ETRS-based model calibration results in a mean Kling–Gupta Efficiency (KGE) value of 0.54 for streamflow simulation; 61% of the river basins have KGE > 0.5 in the validation period, which is consistent with the calibration period and provides a significant improvement over the baseline. Compared to Qobs, the ETRS calibration produces better or similar streamflow simulations in 29% of the basins, while further significant improvements are achieved when either better ET or precipitation observations are used. Furthermore, the model results show better or similar performance in 68% of the basins and outperform the baseline simulations in 90% of the river basins using model parameters from the best ETRS calibration runs. This study confirms that with reasonable precipitation input, the ETRS-based spatially distributed calibration can efficiently tune parameters for better ET and streamflow simulations. The application of ETRS for global scale hydrological model calibration promises even better streamflow accuracy as the satellite-based ETRS observations continue to improve.

scholarly journals Estimation of Land Surface Hydrology in JMA Global Model by Using the Runoff Ratio in Major River Basins

1998 ◽  
Vol 76 (5) ◽  
pp. 817-825
Author(s):  
Kimpei Ichiyanagi ◽  
Masaru Chiba ◽  
Masato Sugi ◽  
Ken-ichi Kuma ◽  
Nobuo Sato
Keyword(s):  
Land Surface ◽  
River Basins ◽  
Global Model ◽  
Surface Hydrology ◽  
Major River ◽  
Land Surface Hydrology

Historical and projected climate change over three major river basins in China from CMIP5 and CMIP6 models

2021 ◽  
Author(s):  
Xian Zhu ◽  
Zhenming Ji ◽  
Xiaohang Wen ◽  
Shao‐Yi Lee ◽  
Zhigang Wei ◽  
...  
Keyword(s):  
Climate Change ◽  
River Basins ◽  
Major River
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