Evapotranspiration Variability and Its Association with Vegetation Dynamics in the Nile Basin, 2002–2011

Alemu, Henok; Senay, Gabriel B.; Kaptué, Armel T.; Kovalskyy, V.

doi:10.3390/rs6075885

Cited by 39 publications

(30 citation statements)

References 68 publications

(98 reference statements)

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“…This has been depicted by a relatively strong correlation (r = 0.81) between the SSEBop ET and NDVI across several land-cover classes in the Mara Basin. The good correlations obtained in this study are stronger than the correlations reported for similar land covers in Alemu et al [10] in the Nile Basin, using a similar SSEBop algorithm.…”

Section: Seasonality Of Etcontrasting

confidence: 52%

“…Their comparisons with observed ET from flux towers showed a better performance of MOD16 for cropland and woody savanna cover than SSEBop, while both models underestimate ET as compared to the observations. Alemu et al [10] also compared ET for the Nile Basin using MOD16-NB and the U.S. Geological Survey (USGS) SSEBop product for Africa and marked similar observations. On the other hand, our results show that SSEBop ET is higher than the MOD16-NB for wetland and flood plain areas and for forest covers.…”

Section: Validationmentioning

confidence: 64%

“…On average, SSEBop ET is 232 mm/yr higher than MOD16-NB for wetlands or water mixed land cover. Similarly, Alemu et al [10] showed a large difference for wetlands in the Nile Basin. The SSEBop ET (1286 mm/yr) is comparable with the SEBAL ET estimates for wetlands and swamps in the Upper Pangani Basin (Kenya/Tanzania) (1291 mm/yr) [60], suggesting the better reliability of our estimates.…”

Section: Validationmentioning

confidence: 99%

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Evapotranspiration Mapping in a Heterogeneous Landscape Using Remote Sensing and Global Weather Datasets: Application to the Mara Basin, East Africa

et al. 2017

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Actual evapotranspiration (ET) is a major water use flux in a basin water balance with crucial significance for water resources management and planning. Mapping ET with good accuracy has been the subject of ongoing research. Such mapping is even more challenging in heterogeneous and data-scarce regions. The main objective of our research is to estimate ET using daily Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature and Global Land Data Assimilation System (GLDAS) weather datasets based on the operational simplified surface energy balance (SSEBop) algorithm at a 1-km spatial scale and 8-day temporal resolution for the Mara Basin (Kenya/Tanzania). Unlike previous studies where the SSEBop algorithm was used, we use a seasonally-varying calibration coefficient for determining the "cold" reference temperature. Our results show that ET is highly variable, with a high inter-quartile range for wetlands and evergreen forest (24% to 29% of the median) and even up to 52% of the median for herbaceous land cover and rainfed agriculture. The basin average ET accounts for about 66% of the rainfall with minimal inter-annual variability. The basin scale validation using nine-years of monthly, gridded global flux tower-based ET (GFET) data reveals that our ET is able to explain 64% of the variance in GFET while the MOD16-NB (Nile Basin) explains 72%. We also observe a percent of bias (PBIAS) of 1.1% and 2.8%, respectively for SSEBop ET and MOD16-NB, indicating a good reliability in the ET estimates. Additionally, the SSEBop ET explains about 52% of the observed variability in the Normalized Difference Vegetation Index (NDVI) for a 16-day temporal resolution and 81% for the annual resolution, pointing to an increased reliability for longer aggregation periods. The annual SSEBop ET estimates are also consistent with the underlying primary (i.e., water and energy) and secondary (i.e., soil, topography, geology, land cover, etc.) controlling factors across the basin. This paper demonstrated how to effectively estimate and evaluate spatially-distributed and temporally-varying ET in data-scarce regions that can be applied elsewhere in the world where observed hydro-meteorological variables are limited.

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Section: Seasonality Of Etcontrasting

confidence: 52%

Section: Validationmentioning

confidence: 64%

Section: Validationmentioning

confidence: 99%

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Evapotranspiration Mapping in a Heterogeneous Landscape Using Remote Sensing and Global Weather Datasets: Application to the Mara Basin, East Africa

et al. 2017

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“…Potential evapotranspiration (PET) and evapotranspiration (ET) were used to represent the water-energy dynamics of land, considering their vital roles in global climate dynamics and terrestrial ecosystem productivity dynamics [12,[14][15][16]. PET and ET represent good predictors of species richness patterns [9] but are not consistent.…”

Section: Water-energy Dynamics and Remote Sensing Datasetsmentioning

confidence: 99%

Effect of the Long-Term Mean and the Temporal Stability of Water-Energy Dynamics on China’s Terrestrial Species Richness

Cai

Guo

et al. 2017

IJGI

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Water-energy dynamics broadly regulate species richness gradients but are being altered by climate change and anthropogenic activities; however, the current methods used to quantify this phenomenon overlook the non-linear dynamics of climatic time-series data. To analyze the gradient of species richness in China using water-energy dynamics, this study used linear regression to examine how species richness is related to (1) the long-term mean of evapotranspiration (ET) and potential evapotranspiration (PET) and (2) the temporal stability of ET and PET. ET and PET were used to represent the water-energy dynamics of the terrestrial area. Changes in water-energy dynamics over the 14-year period (2000 to 2013) were also analyzed. The long-term mean of ET was strong and positively (R 2 ∈ ( 0.40 ∼ 0.67), p < 0.05) correlated with the species richness gradients. Regions in which changes in land cover have occurred over the 14-year period (2000 to 2013) were detected from long-term trends. The high level of species richness in all groups (birds, mammals, and amphibians) was associated with relatively high ET, determinism (i.e., predictability), and entropy (i.e., complexity). ET, rather than PET or temporal stability measures, was an effective proxy of species richness in regions of China that had moderate energy (PET > 1000 mm/year), especially for amphibians. In addition, predictions of species richness were improved by incorporating information on the temporal stability of ET with long-term means. Amphibians are more sensitive to the long-term ET mean than other groups due to their unique physiological requirements and evolutionary processes. Our results confirmed that ET and PET were strongly and significantly correlated with climatic and anthropogenic induced changes, providing useful information for conservation planning. Therefore, climate management based on changes to water-energy dynamics via land management practices, including reforestation, should be considered when planning methods to conserve natural resources to protect biodiversity.

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“…and focused on relative spatial patterns rather than on absolute ET values, the uncertainties of the MODIS ET were considered minimal. In addition, systematic errors of remote sensing data have little impact on long-term anomalies [5].…”

Section: General Approachmentioning

confidence: 99%

Evaluation of Spatio-Temporal Patterns of Remotely Sensed Evapotranspiration to Infer Information about Hydrological Behaviour in a Data-Scarce Region

Wambura

Dietrich

Lischeid

2017

Water

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Information about the hydrological behaviour of a river basin prior to setting up, calibrating and validating a distributed hydrological model requires extensive datasets that are hardly available for many parts of the world due to insufficient monitoring networks. In this study, the focus was on prevailing spatio-temporal patterns of remotely sensed evapotranspiration (ET) that enabled conclusions to be drawn about the hydrological behaviour and spatial peculiarities of a river basin at rather high spatial resolution. The prevailing spatio-temporal patterns of ET were identified using a principal component analysis of a time series of 644 images of MODIS ET covering the Wami River basin (Tanzania) between the years 2000 and 2013. The time series of the loadings on the principal components were analysed for seasonality and significant long-term trends. The spatial patterns of principal component scores were tested for significant correlation with elevations and slopes, and for differences between different soil texture and land use classes. The results inferred that the temporal and spatial patterns of ET were related to those of preceding rainfalls. At the end of the dry season, high ET was maintained only in areas of shallow groundwater and in cloud forest nature reserves. A region of clear reduction of ET in the long-term was related to massive land use change. The results also confirmed that most soil texture and land use classes differed significantly. Moreover, ET was exceptionally high in natural forests and loam soil, and very low in bushland and sandy-loam soil. Clearly, this approach has shown great potential of publicly available remote sensing data in providing a sound basis for water resources management as well as for distributed hydrological models in data-scarce river basins at lower latitudes.

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Evapotranspiration Variability and Its Association with Vegetation Dynamics in the Nile Basin, 2002–2011

Cited by 39 publications

References 68 publications

Evapotranspiration Mapping in a Heterogeneous Landscape Using Remote Sensing and Global Weather Datasets: Application to the Mara Basin, East Africa

Evapotranspiration Mapping in a Heterogeneous Landscape Using Remote Sensing and Global Weather Datasets: Application to the Mara Basin, East Africa

Effect of the Long-Term Mean and the Temporal Stability of Water-Energy Dynamics on China’s Terrestrial Species Richness

Evaluation of Spatio-Temporal Patterns of Remotely Sensed Evapotranspiration to Infer Information about Hydrological Behaviour in a Data-Scarce Region

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