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This study aimed at monitoring, mapping, and assessing the land degradation in the upper Mesopotamian plain of Iraq. The country suffers severely due to land degradation and desertification problems, especially in its central and southern parts. Five vegetative, soil, and water indices related to land degradation were applied to two Landsat TM and ETM+ imageries to assess the extent of land degradation for the study area during the period from 1990 to 2000. A computerized land degradation severity assessment was adopted using ERMapper 7.1, Erdas Imagine 9.2, ArcView 3.3, and ArcGIS 9.1 environments to process, manage, and analysis the raster and thematic datasets. The indices used in this research are: The Normalized Difference Vegetation Index "NDVI", The Normalized Differential Water Index "NDWI", Tasseled Cap Transformation Wetness "TCW", and a new index proposed in this study that is the Normalized Differential Sand Dune Index "NDSDI". The results showed a clear deterioration in vegetative cover (2620.4 km 2 ), an increase of sand dune accumulations (1018.8 km 2 ), and a decrease in soil/vegetation wetness (1720.4 km 2 ), accounting for 12.9, 5.0, and 8.5 percent, respectively, of the total study area. In addition, a decrease in the water bodies area was detected (228.1 km 2 ). Sand dunes accumulations had increased in the total study area, with an annual increasing expansion rate of (10.2 km 2 year -1 ) during the ten years covered by the study. The land degradation risk in the study area has increased by 111% during the study period. The statistical analysis of the results indicated that the soil/vegetation wetness is the biggest influence in the process of land degradation in the study area. The high performance of the NDSDI is promising and effective for identifying the sand dunes accumulations in the area of study. This study finds reveals that most of the counties in the study area are exposed to a serious risk of land degradation and drought water bodies.

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Drought has become the most severe natural disaster in many provinces of China. In this paper, evaporative drought index (EDI) has been used to monitor China's surface dryness conditions based on the exponential evapotranspiration (ET) model and Hargreaves equation from JAXA-MODIS Insolation products, GEWEX, NCEP-2 and MODIS NDVI data. The exponential ET model based on the surface net radiation, vegetation index, mean air temperature and diurnal air temperature range (DTaR) has been developed to estimate surface ET of China and has been independently validated using groundmeasured data collected from two sites (Arou and Miyun) in China, indicating that the bias varies from -5.96 to 5.02 W/m 2 . The good agreement between daily estimated and ground-measured ET using ground observation data collected from all 22 sites further supports the validity of the exponential ET model for regional ET estimation. Moreover, EDI is closely correlated to the average soil moisture at 0-10 cm soil depth of the Yongning site with coefficient of determination of R 2 = 0.52. The spatiotemporal patterns of monthly ET and EDI from April to September of 2004 over China are explored and the result indicates EDI is accordant with the precipitation by comparing the 15-day smoothed EDI with precipitation over six representative sites. The EDI based on the exponential ET model by integrating energy fluxes in response to soil moisture stress has demonstrated its validity for monitoring China's surface drought events.

Evapotranspiration (ET) plays an important role in exchange of water budget and carbon cycles over the Inner Mongolia autonomous region of China (IMARC). However, the spatial and decadal variations in terrestrial ET and drought over the IMARC in the past was calculated by only using sparse meteorological point-based data which remain quite uncertain. In this study, by combining satellite and meteorology datasets, a satellite-based semi-empirical Penman ET (SEMI-PM) algorithm is used to estimate regional ET and evaporative wet index (EWI) calculated by the ratio of ET and potential ET (PET) over the IMARC. Validation result shows that the square of the correlation coefficients (R 2) for the four sites varies from 0.45 to 0.84 and the root-mean-square error (RMSE) is <0.78 mm. We found that the ET has decreased on an average of 4.8 mm per decade (p = 0.10) over the entire IMARC during 1982-2009 and the EWI has decreased on an average of 1.1% per decade (p = 0.08) during the study period. Importantly, the patterns of monthly EWI anomalies have a good spatial and temporal correlation with the Palmer Drought Severity Index (PDSI) anomalies from 1982 to 2009, indicating EWI can be used to monitor regional surface drought with high spatial resolution. In high-latitude ecosystems of northeast region of the IMARC, both air temperature (T a) and incident solar radiation (R s) are the most important parameters in determining ET. However, in semiarid and arid areas of the central and southwest regions of the IMARC, both relative humidity (RH) and normalized difference vegetation index (NDVI) are the most important factors controlling annual variation of ET.