Annual Rainfall Variability Research Articles

Spatio‐temporal rainfall variability and trend analysis in the Tekeze‐Atbara river basin, northwestern Ethiopia

AbstractSpatial and temporal rainfall variability analysis at a basin scale is essential to understand water availability for sustainable water resource management. This study investigated the spatial distribution and temporal rainfall trend in the Tekeze river basin using daily rainfall data collected from 43 meteorological stations with records from 1960 to 2019. Coefficient of variation, seasonality index (SI) and trend index were used to evaluate monthly, seasonal and annual rainfall variability in the basin. The non‐parametric Mann‐Kendall's test was used to understand any rainfall trends. Results showed that there is moderate annual rainfall variability in the basin. Rainfall variability is higher in the Tsedey, Bega and Belg than kiremt season. SI results showed that majority of the Tekeze river basin is categorized as seasonal, most of the rain occurring in less than 3 months. Overall, Mann‐Kendall's test result revealed that there is no significant annual rainfall trend in the basin except for four stations. The seasonal rainfall characteristics and short duration of rain in the basin indicate that there is a need to implement water harvesting measures during the wet season for use in the dry periods.

Spatiotemporal variability and change in rainfall in the Oti River Basin, West Africa

Abstract Understanding rainwater dispersion in a spatiotemporal context is invaluable toward resourceful water management and a food-secure society. This study, therefore, assessed the variations in rainfall at a spatiotemporal scale in the Oti River Basin of West Africa for observed (1981–2010) and future periods (2021–2050) under the representative concentration pathways (RCPs) 4.5 and 8.5 emission scenarios. Rainfall data from meteorological stations and Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) were used. The percentage changes in rainfall for the peak month as well as for rainy and dry seasons under the two climate scenarios were determined. The coefficient of variation (CV) and the standardized anomaly index (SAI) were used to assess annual variations in rainfall. In general, under both emission scenarios, rainfall is projected to decrease over the study area. However, the amount of rainfall during the peak month (August) for RCP4.5 and RCP8.5 could increase by 0.26 and 9.3%, respectively. The highest SAIs for the observed period were +1.58 (2009) and −2.29 (1983) with the latter showing a relationship with historic drought in the basin. The projected SAI under RCP4.5 and RCP8.5 indicated extremely wet (+2.12) and very wet (+1.91) periods for the years 2037 and 2028, respectively. The study provides relevant information and a chance to aid the design of innovative adaptation measures toward efficient water management and agricultural planning for the basin.

Spatio-Temporal Variability in Hydroclimate over the Upper Yangtze River Basin, China

As global warming produces dramatic climate changes, water management is facing increasingly serious challenges. Given to the process of climate change and its complex effects on watershed hydrology, this paper investigates the spatial and temporal variation characteristics of major climatic factors (i.e., precipitation and temperature) over the upper Yangtze River basin (UYRB), China. The statistical analyses are based on annual and seasonal scales during 1951–2020 with a recorded period of seven decades. The Mann–Kendall nonparametric test and R/S analysis are used to record the temporal trends (past and future) of climate variables; the Pettitt test, standard normal homogeneity test and Buishand test are used to detect the homogeneity in climate series. The sensitivities of the streamflow to climatic parameters are assessed at the watershed scale, especially considering the Three Gorges Dam’s (TGD) effect on changing runoff. The results of the study indicate that the annual precipitation of 29 out of 34 series indicate homogeneity, while 31 out of 34 annual mean temperature series show heterogeneity, with jump points around 1997 in the mean temperature of 20 sites. Detectable changes in precipitation were not observed during 1951–2020; however, the temperature increased significantly in the whole basin on annual and seasonal scales, except for several stations in the eastern part. The magnitude of increase in air temperature in high altitudes (Tibet Plateau) is higher than that in low altitudes (Sichuan Plain) over the last seven decades, and future temperatures continue to sharply increase in high altitudes. The TGD plays an important role in explaining the seasonal variations in streamflow at Yichang station, with streamflow experiencing a sharp increase in winter and spring (dry season) and a decrease in summer and autumn (rainy season) compared to the pre-TGD period. The streamflow variation at an annual scale is mainly regulated by climate fluctuation (variation in precipitation). During the last seven decades, increasing air temperature and decreases in rainfall and runoff signify reduced water resources availability, and the climate tends to be warmer and drier over the basin. The sensitivity of the streamflow to watershed precipitation is higher than that to temperature, with variation in annual rainfall explaining 71% of annual runoff variability.

Distribución espacial y controles ambientales de las represas (tajamares) en el Chaco Árido

Arid regions are characterized by water shortage throughout the year, which constrains both the vegetation growth and the supply of water for livestock consumption. The Arid Chaco (~10 Mha) hosts extensive and low-investment livestock systems based on rainwater harvesting stored in dams (small impoundments) as the main source of water supply. In this study, we characterized the spatial distribution of dams in the Arid Chaco and analyzed their relationship with biophysical variables (e.g. rainfall, vegetation, roads). For these purposes, we used satellite images, vector information and performed multivariate analysis on a spatial grid of 135 cells of 0.25°x0.25°. In total, 7920 dams were identified (1 dam every 1230 ha), with maximum densities of 1 dam every 185 ha but also cells without dams associated with the presence of mountains, salt flats and dunes. Dam density was higher in cells with higher densities of livestock establishments, roads and cattle stock (r=0.63, r=0.56 and r=0.51, respectively; P<0.01 in all cases), and in cells with higher mean annual rainfall and lower interannual rainfall variability (r=0.62 and r=-0.47, respectively; P<0.01 for both cases). Although the mean annual rainfall was the best-associated variable with the distribution of dams at the regional scale, this relationship weakened towards the extremes of the gradient (arid and sub-humid). This may be due to anthropic factors such as the low profitability of livestock systems, the previous land uses or land-use changes. The results of this study represent a first attempt to assess the importance of impoundments in the Arid Chaco. We believe that this study may be useful not only to understand livestock production, but also for future studies related to the conservation of wildlife and the development of rural towns in the region.

EVALUATION OF RAINFALL TRENDS DUE TO CLIMATE CHANGE: A CASE STUDY OF SAMARU, ZARIA

Rainfall is the major source of water for agricultural activities in Nigeria, but there has been a major variation due to climate change. This study is to assess the change in rainfall trend due the impact of climate change in Samaru, Zaria Kaduna State. Rainfall data from 1981 – 2018 (38 years) were collected from the Nigerian Meteorological Agency (NIMET). The data was analyzed using Excel and XL-Statistics to evaluate the mean, standard deviation and coefficient of variation of monthly and annual rainfall and other statistical parameter. The study revealed that there is a significant change in the trend of annual rainfall as the highest rainfall was recorded in year 1994 with a value of 1487 mm and lowest rainfall in 1999 as 440 mm. The highest average monthly rainfall data is between July to September and a peak rainfall in August with an average value of 547 mm. This analysis provide useful information to farmers which can be used a basis for planning annual crop planting and also water resources planning such as in irrigation scheduling.

Climate Variability Patterns and Farmers’ Perceptions of Its Impact on Food Production: A Case Study of the Gelda Watershed in the Lake Tana Basin in Northwest Ethiopia

This study looked at patterns of erratic climate and farmer perceptions in the Gelda watershed of Lake Tana Basin in northwestern Ethiopia. The National Meteorological Agency of Ethiopia provided essential climatic data for the period between 1981 and 2011. A household survey and focus group discussions were also used to understand about local communities’ perceptions of climate variability and its impact on food production. Time series trend analysis of observed rainfall and temperature conditions was detected using linear regression analysis. To compare the means of climatic parameters and determine whether the average difference was significantly different from zero, the paired sampled t-test was used. The study found that the average annual temperature trend increased by 1.1°C, while the amount and distribution of annual and monthly rainfall decreased, varied across the catchment, and fluctuated during the study periods (1981–2011) at mean temperature rise with an average rate of 0.17°C in the last decade. The variability of annual and monthly rainfall in terms of intensity and distribution has decreased and varied across the watershed. The analysis revealed that annual rainfall variability was variable in the upper catchment (CV > 11.7%) and lower catchment (CV > 14.4%). The amount and intensity of temperature, on the other hand, increased throughout the study watershed, despite observed variation both spatially and temporally (stated decades). Farmers’ understanding and expression of climate variability in terms of erratic rainfall distribution, decreasing amount, and increasing temperature over the last three decades, however, matched the observed data. Moreover, farmers are pointed out that high population pressure; deforestation and intensified agriculture are responsible factors for the variability of climate in the study watershed. Therefore, based on the findings, scientist and policymakers has to design appropriate adaptation measures that can tackle the aggravation of climate variability for future.

Seasonal Rainfall Trend and Annual Rainfall Variability Analysis for Selected Meteorological Stations in Bhutan

Seasonal Rainfall Trend and Annual Rainfall Variability Analysis for Selected Meteorological Stations in Bhutan

Spatiotemporal characterization of the annual rainfall variability in the Isser Watershed (Algeria)

Wadi Isser watershed (4149 km2), located in the North of Algeria, has experienced a significant rainfall variability during the last four decades. In order to characterize this variability and determine its spatial extension, by means of the analysis of the rainfall data measured in twenty-seven (27) stations, the following study was conducted. The analysis of the long rainfall series of the reference stations of Bni Slimane (1920–2014) and Djebahia (1923–2014) through the application of three statistical tests (Pettitt, Buishand and Lee and Heghinian) revealed an episode of low rainfall from 1973 to 2001 for the Djebahia station and from 1975 to 2001 for the Bni Slimane station. This period was characterized by a decrease in annual rainfall varying between 14 and 43%, followed by a rainy phase in the watershed with an increase in annual rainfall (35.8%) at the Khebouzia station. The analysis of the kriged maps, developed by geostatistical modeling of the spatial structure of precipitation (1975–2014), supported and corroborated the results of the statistical tests. Indeed, the spatial interpolation based on decadal averages of rainfall from 1975 to 2014 illustrates a well-contrasted spatial variability for the four decades. The northern part of the watershed is characterized by a higher rainfall than the central and southern parts of the watershed. In the light of the results obtained by applying the two approaches mentioned above, a decreasing trend in rainfall is clearly evident from the beginning of the decade 1985–1994. A double rainfall gradient is highlighted with an increase in rainfall from east to west and from north to south. At the same time, there was a surplus towards the end of the third decade and the fourth decade. A return of precipitation is thus highlighted as well as the different breaks in the series. Through this research, the statistical study and the geostatistical mapping have enabled the elaboration of a relevant tool for decision support to the managers in the field of environment and hydraulics, in a general way, and in a context of global warming. In fact, it will allow them to better understand the developments of wadis, the integrated management of water resources in order to guarantee current and future needs for drinking, industrial, and agricultural water in this semi-arid region.

Uncertainty in Drought Identification Due to Data Choices, and the Value of Triangulation

Droughts are complex and gradually evolving conditions of extreme water deficits which can compromise livelihoods and ecological integrity, especially in fragile arid and semi-arid regions that depend on rainfed farming, such as Kitui West in south-eastern Kenya. Against the background of low ground-station density, 10 gridded rainfall products and four gridded temperature products were used to generate an ensemble of 40 calculations of the Standardized Precipitation Evapotranspiration Index (SPEI) to assess uncertainties in the onset, duration, and magnitude of past droughts. These uncertainties were driven more by variations between the rainfall products than variations between the temperature products. Remaining ambiguities in drought occurrence could be resolved by complementing the quantitative analysis with ground-based information from key informants engaged in disaster relief, effectively formulating an ensemble approach to SPEI-based drought identification to aid decision making. The reported trend towards drier conditions in Eastern Africa was confirmed for Kitui West by the majority of data products, whereby the rainfall effect on those increasingly dry conditions was subtler than just annual and seasonal declines and greater annual variation of rainfall, which requires further investigation. Nevertheless, the effects of increasing droughts are already felt on the ground and warrant decisive action.

INERCJA ROCZNEGO ODPŁYWU CAŁKOWITEGO RZEK POLSKI WZGLĘDEM MIĘDZYROCZNEJ ZMIENNOŚCI PRZEBIEGU ELEMENTÓW KLIMATYCZNYCH

The work discusses the formation of the annual total runoff of Polish rivers as a function of changes in the annual values of climatic elements. The results of the analysis show that in the years 1966–2015, 40–50% of the runoff variance in a hydrological year was determined by the variability of climatic elements that occurred in the preceding year, and 20–30% in the same year. This indicates the occurrence of much stronger inertia in the variability of the runoff in relation to the variability of weather conditions. The main elements influencing the variability of the runoff are the annual rainfall and the annual air temperature in the preceding year, and in the same hydrological year – the variability of annual rainfall, sunshine duration and air temperature. The runoff from the area of Poland shows a strong relationship (R = 0.82) with the de Martonne climate aridity indices, the variability of which in the preceding and the current year together explains ~66% of its variance.

Groundwater decline in Central Punjab - Is it a warning?

Central Punjab covers around 40% area of state Punjab. Paddy covers nearly 75% of the total cropped area and requires nearly 800–2000 mm of irrigation water depending upon climate and soil type. The increase in irrigation demand has led to over-exploitation of groundwater in Central Punjab. This study aims to investigate the precipitation, temperature, groundwater and potential evapotranspiration (PET) trends in Central Punjab through an examination of historical climate data covering the past almost twenty years. This study also compared all the contributing factors of groundwater depth decline from 1998 to 2017. In years, when rainfall was above normal in 2008 and 2011, the groundwater depth decline reduced as compared to other years. The maximum (2026 mm) and minimum (1566 mm) PET was observed in 2009 and 2004. Minimum rainfall (422.6 mm) was observed in 2000 and maximum (1012 mm) was observed in 2011. Groundwater Depth was significantly positively associated with paddy area and tubewell density. Fluctuation in groundwater depth is not only due to the variability of annual rainfall but also due to paddy cultivation. Thus, there is a need for wise water management and crop diversification in this study area.

Effect of climate variability on yields of selected staple food crops in northern Ghana

Agriculture in Ghana is vulnerable to the adverse effects of climate variability. This poses a challenge to food security across the country. Despite this vulnerability, limited research has been conducted to understand the effect of climate variability on the yields of staple food crops in Ghana. This study assessed the effect of climate variability on the yields of selected staple food crops (millet, sorghum, rice, groundnut and maize). The study used the Mann-Kendall trend test and multiple regression analysis to assess how climate variability (in annual rainfall, onset, cessation, number of dry days and temperature) has affected the yields of selected food crops in five districts in northern Ghana (Bole, Nanton, Tolon, Kassena Nankana East and Wa) over a 21-year period (1995–2016). Results suggested a marginal decrease in annual rainfall ( p > 0.05) and a significant increase in temperature ( p < 0.05) over the period of study in the districts. Variability in the onset, cessation, length of rainy days and number of dry days was statistically significant from year to year, and also across the districts ( p < 0.05). Results indicated substantial variability in the yields of the selected staple food crops. Temperature, number of dry days, onset, annual rainfall and cessation explained about 43%, 32%, 30%, 25% and 14%, respectively of the variations in the yields of groundnut, sorghum, millet, maize and rice. Our results generally suggest that the changing climate substantially affects food production in the study districts, highlighting the need for adaptations including the use of agricultural diversification and the greater use of drought tolerant varieties of these staple crops, as well as the continuing investment in crop breeding programmes to enhance drought tolerance. • Climatic variables (annual rainfall, onset, cessation, number of dry days and temperature) are erratic in northern Ghana. • Changing climate substantially affects food production in northern Ghana. • Continuing investment in crop breeding programmes to enhance drought tolerance.

High-Resolution North Sulawesi Drought Hazzard Mapping Based on Consecutive Dry Days (CDD)

North Sulawesi is one of the Province in northern Indonesia with high spatial annual rainfall variations and influenced by global climate anomaly that can lead to extreme events and disaster occurrence, such as flood, landslide, drought, etc. The purpose of this study is to generate high-resolution meteorological hazard map based on long-term historical consecutive dry days (CDD) over the North Sulawesi region. CDD was calculated based on observed daily precipitation data from Indonesia Agency for Meteorology, Climatology, and Geophysics (BMKG) surface observation station network (CDDobs) and the daily-improved Climate Hazards group Infrared Precipitation with Stations (CHIRPS) version 2.0 (CDDCHIRPS) during 1981 – 2010 period. The Japanese 55-year Reanalysis (JRA-55) data obtained from iTacs (Interactive Tool for Analysis of the Climate System) with the same time scale period also used to explain physical – dynamical atmospheric properties related to drought hazard over this region. The Geostatistical approach using regression kriging method was applied as spatial interpolation technique to generate high resolution gridded (0.05° × 0.05°) drought hazard map. This method combines a regression of CDDobs as dependent variable (target variable) on CDDCHIRPS as predictors with kriging of the prediction residuals. The results show that most of the areas were categorized as medium drought hazard level with CDD values ranging from 80-100 days. Meanwhile, small islands around main Sulawesi island such as Sangihe and Karakelong island are dominated by low drought hazard levels with CDD values ranging from 50-60 days. The highest levels of drought hazard area are located in South Bolaang Mongondow Regency.

How changes in cropping intensity affect water usage in an irrigated Mediterranean catchment

Agricultural policies and social change influence irrigation management decisions and their associated effects. The changes in the Common Agricultural Policy of the European Union have deeply affected irrigated agriculture in the Mediterranean region. In this region, hydrology is rather complex and the environment particularly vulnerable. We monitored cropping patterns and the water balance in a sprinkler-irrigated catchment in Central Portugal over thirteen irrigation seasons and twelve rainfall seasons. There was wide variation in annual rainfall (from 283 mm to 667 mm) and in the intensity of rainfall events from year to year. A monitoring station at the catchment outlet was installed to measure runoff which, together with field observations, allowed us to compute a water balance for both the rainfed and the irrigation seasons. Changes in cropping intensity led to changes in the depth of irrigation. Irrigation runoff followed irrigation depth and both followed the trend of cropping intensity. Less intensive cropping also reduced the off-site effects of agricultural activities. The runoff coefficient was 0.28 in the rainfed seasons and 0.02 in the irrigation seasons. The changes in the irrigation hydrology and in the off-site effects of agricultural activities in the catchment were caused by changes in cropping intensity induced by the European Union Common Agricultural Policy reforms, rather than by environmental or technical factors.

Preliminary Disease Survey of Domestic Ruminants on Farasan Islands, Saudi Arabia

The Farasan Islands are situated in the Red Sea in southwestern Saudi Arabia Flamand et al. [1]. The climate is arid with low and highly variable annual rainfall Child et al. [2]. Although there are more than 300 islets, only the two largest Farasan Kebir (381km2) and As Saqid (149km2)-are permanently inhabited by humans Flamand et al.

Above‐ground net primary productivity in regenerating seasonally dry tropical forest: Contributions of rainfall, forest age and soil

Abstract Identifying factors controlling forest productivity is critical to understanding forest‐climate change feedbacks, modelling vegetation dynamics and carbon finance schemes. However, little research has focused on productivity in regenerating tropical forests which are expanding in their fraction of global area have an order of magnitude larger carbon uptake rates relative to older forest. We examined above‐ground net primary productivity (ANPP) and its components (wood production and litterfall) over 10 years in forest plots that vary in successional age, soil characteristics and species composition using band dendrometers and litterfall traps in regenerating seasonally dry tropical forests in northwestern Costa Rica. We show that the components of ANPP are differentially driven by age and annual rainfall and that local soil variation is important. Total ANPP was explained by a combination of age, annual rainfall and soil variation. Wood production comprised 35% of ANPP on average across sites and years, and was explained by annual rainfall but not forest age. Conversely, litterfall increased with forest age and soil fertility yet was not affected by annual rainfall. In this region, edaphic variability is highly correlated with plant community composition. Thus, variation in ecosystem processes explained by soil may also be partially explained by species composition. These results suggest that future changes in annual rainfall can alter the secondary forest carbon sink, but this effect will be buffered by the litterfall flux which varies little among years. In determining the long‐term strength of the secondary forest carbon sink, both rainfall and forest age will be critical variables to track. We also conclude that detailed understanding of local site variation in soils and plant community may be required to accurately predict the impact of changing rainfall on forest carbon uptake. Synthesis. We show that in seasonally dry tropical forest, annual rainfall has a positive relationship with the growth of above‐ground woody tissues of trees and that droughts lead to significant reductions in above‐ground productivity. These results provide evidence for climate change—carbon cycle feedbacks in the seasonal tropics and highlight the value of longitudinal data on forest regeneration.

Assessment of the Impact of Rainfall Variability on Drinking Water Production at Treatment Plants in Nzoia River Basin, Kenya

Increased wet season rainfall is associated with improved water supply at point water sources and improved river flows and water reservoir levels. For piped water supply schemes with surface water intakes, this is supposed to enhance operations since there is adequate raw water unlike in the dry season where operations are interrupted due to insufficient flows. However, this is not the case in Nzoia River Basin as established by this study. As rainfall increases, drinking water production in treatment plants at Moi’s Bridge, Lumakanda and Busia water supplies decrease and vice versa. Nzoia River Basin is one of the regions that is highly vulnerable to climate variability in Kenya, hence understanding rainfall variability and trends is important for better water resources management and especially drinking water supply. This study aimed at assessing rainfall variability and trends for 3 rainfall stations in Nzoia River Basin; Leissa Farm Kitale, Webuye Agricultural Office and Bunyala Irrigation Scheme and its impact on drinking water production at Moi’s Bridge, Lumakanda and Busia water supplies treatment plants. The rainfall data used in this study covers 31 years period from 1970 to 2001 and was obtained from the Kenya Meteorological Department (KMD), Nairobi, Kenya. Monthly water supply production data for Moi’s Bridge, Lumakanda and Busia water supplies covering 15 years period from 2000 to 2014 was obtained from the County governments of Uasin Gishu, Kakamega and Busia. Rainfall variability and trend was analysed using the parametric test of Linear regression analysis and the non-parametric Mann Kendall statistical test. Monthly rainfall and monthly drinking water production was analysed using Pearson moment correlation to establish the relationship between monthly rainfall and monthly drinking water supply production at Mois Bridge, Lumakanda and Busia Water supplies treatment plants. The results of variability and trend in annual rainfall shows Webuye Agricultural Office recording declining rainfall at -0.8994 mm/31 years (-0.029 mm/ year); whereas Leissa Farm Kitale shows increasing rainfall at 1.0325 mm/31 years (0.033 mm/ year) and Bunyala Irrigation Scheme’s rainfall is increasing at 0.5245 mm/31 years (0.017 mm/ year). Drinking water supply production at Moi’s Bridge, Lumakanda and Busia water supplies has been increasing with time between 2000 and 2014. The results of Pearson moment correlation coefficient shows a strong negative relationship between monthly rainfall and monthly drinking water supply production at 0.05 significance level for Moi’s Bridge, Lumakanda and Busia water supplies. This shows that as rainfall increases, drinking water supply production in treatment plants at Moi’s Bridge, Lumakanda and Busia water supplies decreases. During the rainy season, the cost of water treatment goes up as a result of increased turbidity. Increased rainfall in Nzoia River Basin presents water treatment challenges to the existing water supply treatment plants resulting into reduced production.Water supply managers should improve the capacity of the existing water supply treatment plants to cope with the increased rainfall variability under the changing climatic conditions.

Annual rainfall variation and dispersal limitation combine to alter invaded plant community diversity, dominance hierarchies and seeding phenology

Natural ecosystems are threatened by climate change, fragmentation, and non-native species. Dispersal-limitation potentially compounds impacts of these factors on plant diversity, especially in isolated vegetation patches. Changes in climate can impact the phenology of native species in distinct ways from non-natives, potentially resulting in cascading impacts on native communities. Few empirical studies have examined the combined effects of climate change and dispersal limitation on community diversity or phenology. Using a five-year dispersal-restriction experiment in an invaded semi-arid annual plant system in Western Australia, we investigated the interactive effects of dispersal-restriction and inter-annual rainfall variation on community composition, species dominance and seed production timing. We found inter-annual rainfall variation to be the principal driver of community dynamics. Drought years had long-term, stable effects on community composition, with evidence of shifts from native toward non-native dominance. Surprisingly, community composition remained largely unchanged under dispersal restriction. A subtle ‘dispersal rescue’ effect was evident for a dominant native annual forb and a dominant annual non-native grass but only in average rainfall years. The timing of seed production was primarily driven by annual rainfall with native and non-native grasses having opposite responses. There was no evidence that inter-annual variation in seeding timing affected community diversity over time. Our study demonstrates that dispersal is not a major factor in driving community diversity in this invaded, semi-arid system. Results do suggest, however, that increases in drought frequency likely benefit non-native species over natives in the long term.

Hydro-climatic Variability and Trend Analysis of Modjo River Watershed, Awash River Basin of Ethiopia

Climate change and variability is expected to trigger changes in temperature and precipitation series. This study aimed at assessing variability and trend of hydro-climatic variables at Modjo River watershed. Long-term climate data of 5 representative stations with in the watershed (1981-2010) and streamflow data of Modjo gauging station (1983 -2010) were used. Rainfall variability was analyzed using Coefficient of variation (CV), Precipitation concentration index (PCI) and Standardized anomaly index (SAI). Climate trends were evaluated using Sen’s slope estimator and Mann–Kendall trend test methods. The study revealed Most of the stations showed low variation in annual rainfall (CV% &lt;20) while the main (Kiremt) and short (Belg) season rainfall exhibited CV ranging from low to high. Both annual and seasonal rainfall showed a non-significant trend at all stations for the past 30 years. However, majority of stations showed an increasing trend in annual daily average temperature ranging from 0.2 to 0.6ºC per decade. Following increases in temperature and the subsequent rise in evapotranspiration, streamflow has shown a high significant declining trend. The temporal decline in streamflow at Modjo watershed could likely affect downstream Koka dam water reserve. Thus, any watershed management strategy that can optimize water conservation for sustainable crop production and option that can improve flow to the reserve is vital. Keywords: Climate change, Climate variability, Hydro-climate, trend, Modjo river watershed DOI: 10.7176/JEES/11-9-04 Publication date: September 30 th 2021

Spatial and temporal trends and variability of rainfall using long-term satellite product over the Upper Blue Nile Basin in Ethiopia

The present study aimed to analyze the long-term trends and variability of rainfall in the Upper Blue Nile (UBN) basin in Ethiopia using Climate Hazards Group Infrared Precipitation with Stations (CHIRPS-v2) rainfall product from 1981 to 2018. A pixel-based rainfall variability and trend analysis was made at the annual, seasonal, and monthly temporal scales. The coefficient of variation (CV) was applied to compute the rainfall variability. The trends for each pixel were analyzed using Mann–Kendall (MK) trend test, while the Theil-Sen slope was used to estimate the magnitude of the trend. Results indicated that monthly and seasonal rainfall variabilities are high with the CV up to 140% and 70%, respectively. Annual rainfall variability was found to be low with CV ranging from 6 to 18%. The annual rainfall anomaly analysis, on the other hand, indicated that there are variations in the amount of rainfall received at different years and parts of the basin. It captured the spatial distributions of below- and above-average rainfall periods and its associated drought and flood events, respectively, observed in the basin. In general, the MK monotonic trend analysis for the annual, summer, spring, and autumn rainfall over the entire basin showed an average increasing trend at a rate of 2.48 mm year−1,1.16 mm year−1, 0.92 mm year−1, and 0.67 mm year−1, respectively. In contrast, the rainfall average trend during the winter season (− 0.15 mm year−1) indicated a decreasing trend. The consistency of per-pixel trends with previous studies, based on rain gauge observations, demonstrates the robustness of the trends. Furthermore, the completely raster-based analysis made in this study has provided essential information regarding the spatial variability and trends of rainfall in the basin, which was not satisfactorily captured by the conventional systems due to the larger inter-station distance between rain gauges. Thus, this could be a valuable addition to the existing knowledge of rainfall characteristics in the UBN basin.