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Understanding the spatial variability of groundwater recharge in response to distributed Land-use, soil texture, topography, groundwater level, and hydrometeorological parameters is significant when considering the security of groundwater resource development. Thus, this study was aimed at estimating the spatial groundwater recharge of Raya valley, northern Ethiopia using spatially distributed water balance model (WetSpass). Input data for the model were prepared in the form of grid maps using 90 m grid size and the parameter attribute tables were adjusted to represent the Raya valley condition using expert knowledge and scientific literatures. The results of the model indicated that the long-term temporal and spatial average annual rainfall of 710 mm was partitioned as 57 mm (8%) of surface runoff, 598 mm (84%) of evapotranspiration, and 55 mm (8%) of recharge. The recharge corresponds to 137 million cubic meters (Mm3) for the Raya basin (with area of about 2500 km2) from which 84% of the recharge takes place during summer season, while the remaining 16% takes place during the winter (dry) season. The analysis of the simulated result showed that WetSpass works well to simulate water balance components of Raya valley and is especially suitable for studying the effects of Land-use changes on the water regime in the basin.

The daily rainfall is the most important and demanded input of water resources studies, challenged by typically low density and/or poor quality of in-situ observations. However, the satellite earth observation, through freely available web-based products, can provide complementary rainfall data. Such data is however, typically affected by substantial error, particularly at daily temporal resolution. Therefore, effective methods and protocols of rainfall downscaling, validation, and bias-correction are needed. The aims of this study were to: i) validate two downscaled satellite-derived daily rainfall products, CHIRPS and MPEG, against in-situ observations; ii) merge the downscaled products with in-situ observations to improve their accuracy and evaluate them to select better performing one. This study was conducted at topographically complex, Upper Tekeze Basin (UTB), separately for the wet and dry seasons, within 1 January 2015 – 31 December 2018. Validation of the products, downscaled by nearest-neighbor (NN) and bilinear (BL) methods, was carried out using descriptive statistics, categorical statistics and bias decomposition methods, introducing novel protocol with new bias indicators for each of the evaluation methods. The validation showed large biases of CHIRPS and of MPEG, larger for CHIRPS than for MPEG, larger in dry than in wet season and slightly larger for NN than for BL. To correct biases of the downscaled CHIRPS and MPEG, each was merged with the in-situ observed rainfall applying Geographically Weighted Regression (GWR) algorithm and using rainfall dependence on altitude as explanatory variable. The GWR-merging method substantially improved the accuracy of the MPEG and CHIRPS, with slightly better final accuracy of MPEG than of CHIRPS, better in wet than in dry season. This study confirmed that GWR-merged method could substantially reduce daily bias of satellite rainfall products, even in topographically complex areas, such as the UTB. Further improvement of the method application, can be achieved by densifying rain-gauge network and eventually by adding accuracy-effective explanatory variable(s).

Climate indices are the diagnostic tools used to define the state of climate system. The main objective of this study was to investigate the climate index change in future time periods in the upper Baro basin of Ethiopia. The daily precipitation and maximum and minimum temperature data were downscaled using Statistical Downscaling Model (SDSM). The precipitation and temperature data were estimated according to UK Hadley Centre Coupled Model version 3 (HadCM3) global circulation model with medium-high (A2) and medium-low emission (B2) scenarios in three future time interval periods. The De Martonne Aridity Index and Pinna Combinative Index change of the future time periods centered at 2020s, 2050s, and 2080s was computed. The analysis was based on percentage change between the baseline and three future time periods. The monthly De Martonne Aridity Index result showed that there are months in the dry season classified as semi-dry with value of less than 20 and the land needs irrigation in these months. The Pinna Combinative Index value also showed the same trend like that of the De Martonne Aridity Index and a high correlation coefficient was noticed, verifying similar trend of the two indices for the three future time period changes. Overall, humidity is expected to decrease in most of the months in the three future time periods for both A2 and B2 emission scenarios because of the increment of temperature in the future.

Information on the rate and pattern of urban expansion is required by urban planners to devise proper urban planning and management policy directions. This study evaluated the dynamics and spatial pattern of Mekelle City’s expansion in the past three decades (1984–2014). Multi-temporal Landsat images and Maximum Likelihood Classifier were used to produce decadal land use/land cover (LULC) maps. Changes in LULC and spatial pattern of urban expansion were analysed by post-classification change detection and spatial metrics, respectively. The results showed that in the periods 1984–1994, 1994–2004, and 2004–2014, the built-up area increased annually by 10%, 9%, and 8%, respectively; with an average annual increment of 19% (100 ha year−1), from 531 ha in 1984 to 3524 ha in 2014. Between 1984 and 2014, about 88% of the gain in built-up area was from conversion of agricultural lands, which decreased by 39%. Extension of existing urban areas was the dominant growth type, which accounted for 54%, 75%, and 81% of the total new development during 1984–1994, 1994–2004, and 2004–2014, respectively. The spatial metrics analyses revealed urban sprawl, with increased heterogeneity and gradual dispersion in the outskirts of the city. The per capita land consumption rate (ha per person) increased from 0.009 in 1984 to 0.014 in 2014, indicating low density urban growth. Based on the prediction result, the current (2014) built-up area will double by 2035, and this is likely to have multiple socioeconomic and environmental consequences unless sustainable urban planning and development policies are devised.

Exclosures are established with the objective of rehabilitating degraded lands and restoring of woody vegetation. Various studies have been conducted to evaluate the success of exclosure on restoring woody species diversity. However, works focusing on the effect of topographic factors on woody species diversity are scarce. Understanding the factors that determine woody species diversity is important for management purposes. Therefore, this paper analyzes the effect of altitude, slope, and aspect as topographic variables on woody species diversity in Dawsura exclosure in northern Ethiopia. Data on species identity, abundance, slope, elevation and aspect were recorded from 58 sampling plots. Different diversity indices were used to analyze the data and one-way ANOVA and linear regression was conducted. There were a total of 34 woody species represented 15 families, of which 62% and 38% were trees and shrubs respectively. Altitude (r2 = 0.63, p = 0.000 and r = 0.794, p < 0.01) and slope (r2 = 0.57, p = 0.002 and r = 0.68, p < 0.01) correlated significantly and positively with Shannon diversity, whereas aspect (r2 = 0.12, p = 0.378 and r = 0.27, p > 0.05) did not correlate significantly with Shannon diversity. Woody species diversity at moderate (1.44) and high (1.85) altitudes was significantly different from that of low (0.86) altitude areas (p = 0.0013). Furthermore, significantly higher woody species diversity was recorded at steep slope (1.88) and moderately steep slope (1.62) areas as compared to the gentle slope (0.95) areas. No significant variation was observed in woody species diversity among the aspect categories (p > 0.05). The study concludes that woody species diversity is largely regulated by slope and altitude than aspect in the exclosure. We suggest other environmental and anthropogenic variables should be taken into consideration in future studies on woody species diversity., Environmental science; Ecology; Environmental assessment; Environmental health; Environmental management; Environmental pollution; Exclosure; Topographic variables; Diversity; Woody species

This study investigated the influence of topographic variability on land use land cover (LULC) change in Hugumburda national forest priority area. The study was based on three periods of LULC maps derived from satellite imageries: Landsat TM for 1985, Landsat ETM+ for 2000 and Landsat OLI for 2015, and topographic attributes derived from ASTER digital elevation model. Supervised image classification was carried out using Maximum Likelihood classifier algorithm. Changes in LULC vis-a-vis topographic variability (altitude, slope and aspect) were assessed based on overlay analysis in a GIS environment. Six LULC classes were identified with an overall accuracy of 93% and Kappa statistics of 0.90. Shrubland and forest land were the dominant LULC types which respectively accounted for about 36% and 26% in 1985 and 39% and 33% in 2000. Forest land (35%) followed by shrubland (30%) continued to be the dominant LULC types in 2015. Between 1985 and 2015, about 23% of the study area showed changes in LULC which constitute increase in forest cover by about 715 ha mainly at the expense of shrubland. Steep slopes, higher altitudes and Northeast aspect were important topographic attributes where marked increased in forest cover was observed. The increase in forest cover along steep slopes, higher altitudes and Northeast aspect can be used to stimulate further expansion of forest cover along similar topographic conditions. This study demonstrated that topographic variability plays an important role in controlling LULC changes. Detailed investigation of drivers of the increased in forest cover is required to scale up the success in other regions with similar climatic and topographic settings.