Contribution Of Climate Variability Research Articles

Contribution of climatic variables and their interactions to reference evapotranspiration changes considering freeze-thaw cycles in the Tibetan Plateau during 1960–2022

While the direct impact of climate change on reference evapotranspiration (ET0) has been extensively studied, there is limited research on the indirect impact resulting from the interaction between climatic variables. This gap hinders a comprehensive understanding of climate change effects on ET0. Additionally, there is scarce exploration into the quantitative effect of freeze-thaw cycles on ET0 variation. In this study, we employed path analysis and dependent variable variance decomposition methods to discern the direct and interactive effects of climatic variables on ET0 in the Tibetan Plateau from 1960 to 2022. Annual ET0 exhibited variation across basins, with the coefficient of variability during the thawed period smaller than that during the non-thawed period. On an annual scale, the largest contribution to ET0 variation came from water vapor pressure deficit (VPD) at 47.7%. This contribution was amplified by its coupled interaction with temperature (T) at 47.1%, although the contribution was partially offset by the interactive effects of VPD with downward shortwave radiation and wind speed at −2.4% and − 27.6%, respectively. During different freezing-thawing periods, VPD primarily controlled ET0 variation, with its interaction with other climatic variables enhancing its impact. Furthermore, soil moisture, influenced by freeze-thaw cycles, exhibited a strong correlation with T and VPD, indicating the significant effect of freeze-thaw cycles on ET0 variation. The weak correlation between ET0 and NDVI suggested that vegetation growth had a limited regulatory effect on ET0. These findings provide valuable insights into the impact of interactions between climatic variables on hydrological processes, enhancing our understanding of the interactive roles of hydrometeorological variables.

Quantitative Analysis of Climate Variability and Human Activities on Vegetation Variations in the Qilian Mountain National Nature Reserve from 1986 to 2021

Rapid climate variability and intense human activities generate obvious impacts on the Qilian Mountains ecosystem. The time series of fractional vegetation coverage (FVC) from 1986 to 2021 were used to quantify the impact of climate variability and human activities on vegetation variations in the Qilian Mountain National Nature Reserve (QMNNR), using 3147 land satellite images based on the Google Earth Engine cloud platform. The contributions of climate variability and human activities to FVC were quantified using multiple regression residual analysis. Partial correlation and correlation methods were used to quantify the impact of temperature, precipitation, and human activity footprints on FVC. The results showed that from 1986 to 2021, the increase rate of FVC was 1.7 × 10−3 y−1, and the high vegetation coverage of the FVC was mainly distributed in the southeastern part of the reserve. In contrast, the low vegetation coverage was mainly distributed in the northwest part of the reserve. The Mann–Kendall mutation test found that the year of 2009 was the year of the mutation. The growth rate of FVC from 2010 to 2021 was greater than that from 1986 to 2009. In addition, climate variability and human activities exhibited a remarkable spatial heterogeneity in FVC changes. Climate variability and human activities contributed 49% and 51% to the increase in FVC in the reserve, respectively, and the contribution of human activities was greater than that of climate variability. The warming and humidification phenomena in the reserve were obvious. However, precipitation was the dominant factor affecting the dynamic changes in FVC. This study improves our understanding of the response of vegetation dynamics to the climate and human activities in the QMNNR.

Contributions of Climate Variability and Anthropogenic Activities to Confined Groundwater Storage in Hengshui, North China Plain

Groundwater storage (GWS) in confined aquifer systems is often influenced by climate variability and anthropogenic activities, and it is vital to quantify their contributions for the purpose of groundwater management and surface water allocation plans. In this study, we characterize the spatiotemporal evolution of the GWS in confined aquifer systems across Hengshui, North China Plain, and investigate its relationships with changing climate conditions and human activities through the integration of InSAR-derived surface displacements with hydraulic head observations and precipitation data, during 2004–2010 and 2016–2020. Our results indicate that the GWS in confined aquifer systems decreased markedly by 4.59 ± 0.35 km3 with an accelerating trend during the study period. The GWS variations show a strong correlation with precipitation during irrigation periods (March to July), and hence, the climate and anthropogenic-driven GWS variations can be separated from each other with a linear model. We find that the GWS depletion caused by climate variability and anthropogenic activities were −0.31 ± 0.10 km3 and −4.28 ± 0.40 km3, respectively, during the study period. The mean contribution of anthropogenic activities to the GWS variations was −71.9%, implying that the GWS variations in confined aquifer systems were primarily anthropogenic driven. It is also found that the well observations alone poorly characterize the spatiotemporal evolution of the GWS due to their limited spatial density, and the integrated InSAR/well approach appears to be promising for overcoming this challenge.

Exploration of the Contribution of Fire Carbon Emissions to PM2.5 and Their Influencing Factors in Laotian Tropical Rainforests

It is of great significance to understand the drivers of PM2.5 and fire carbon emission (FCE) and the relationship between them for the prevention, control, and policy formulation of severe PM2.5 exposure in areas where biomass burning is a major source. In this study, we considered northern Laos as the area of research, and we utilized space cluster analysis to present the spatial pattern of PM2.5 and FCE from 2003–2019. With the use of a random forest and structural equation model, we explored the relationship between PM2.5 and FCE and their drivers. The key results during the target period of the study were as follows: (1) the HH (high/high) clusters of PM2.5 concentration and FCE were very similar and distributed in the west of the study area; (2) compared with the contribution of climate variables, the contribution of FCE to PM2.5 was weak but statistically significant. The standardized coefficients were 0.5 for drought index, 0.32 for diurnal temperature range, and 0.22 for FCE; (3) climate factors are the main drivers of PM2.5 and FCE in northern Laos, among which drought and diurnal temperature range are the most influential factors. We believe that, as the heat intensifies driven by climate in tropical rainforests, this exploration and discovery can help regulators and researchers better integrate drought and diurnal temperature range into FCE and PM2.5 predictive models in order to develop effective measures to prevent and control air pollution in areas affected by biomass combustion.

Estimation of productivity yield gap contributions of climate change variability in selected horticultural crops (fresh maize and okra) in Anambra State, Nigeria

Most horticultural crops are susceptible to climate extremes that affect vegetative growth and yield. Climate variability poses a great threat to food security and the sustainability of the agricultural sector in Nigeria. However, the study estimated the productivity yield gap contributions of climate variability among maize and okra farmers. Data was collected from a cross-section of 160 farmers. Statistical tools such as descriptive statistics, second-order quadratic and linear regression models and Chi-square were utilized to operationalize the study objectives. The study established that high temperature was the highest climate variability (okra - 80.0%, and maize - 78.7%); whereas fug was lowest with 38.3% (okra) and 30.4% (maize). Again, flood contributed to the highest (27.5% - okra, and 36.5% - maize) yield gap. All the climate variability cumulatively explained 6.49 ton/ha (maize) and 3.47 ton/ha (okra) yield gap. However, the farmers are producing 2.26 ton/ha (maize) and 1.70 ton/ha (okra) below their optimal level. For better management, the study revealed that sex, age, education, household size, and cooperative membership are responsible for okra farmers; while age, marital status, and farming experience are responsible for maize farmers’ managerial ability. The study, therefore, concludes that climate variability significantly reduced horticultural crop yield. Howbeit, the study recommends that farmers should be taught to adopt climate-smart agricultural practices.

Changes in atmospheric CO2 concentration over the past two millennia: contribution of climate variability, land-use and Southern Ocean dynamics

Changes in atmospheric CO2 concentration over the past two millennia: contribution of climate variability, land-use and Southern Ocean dynamics

The impact of climate variables on nutmeg (Mirystica fragrans HOUTT) production in Saparua Island, Central Maluku Regency

Nutmeg is a prime estate commodity that has high economic value, a major source of income for farmers in some areas of Maluku as well as a source of Indonesian foreign exchange through export. Nutmeg is originally from Banda archipelago, Maluku, Indonesia. Nutmeg grows in specific areas with certain agroclimatic condition, therefore climate as an environmental factor plays an important role in nutmeg production. The objective of this study was to determine the influence of climate variables on the productivity of nutmeg in Saparua Island. The study was conducted in Saparua Island, Central Maluku Regency from April to October 2017. Survey method was used in this study. Three villages were chosen purposively since they are the center of nutmeg production on the island. Direct observations were done in the fields as well as interviewing key respondents. Statistical and climate data was obtained from related institutions. Rainfall trend was analyzed to determine climate change and regression analysis was done to see the relationship between climate variables (air temperature, air relative humidity and annual rainfall) with nutmeg production in the last 10 years. The result showed that there has been an increased in total rainfall of 374 mm (13.0%) in the study area in the period of the last 30 years (1987-2016) compared with the previous period (1957-1986) which indicates there has been climate change in Saparua island. The contribution of climate variables (air temperature, air relative humidity and rainfall) to nutmeg production were 45.52%; 37.13% and 55.12% respectively.

Увеличение вклада климатических переменных в объяснение изменчивости биомассы деревьев дуба на территории Евразии в связи с отклонением модели от аллометрии

Лесные экосистемы, являясь поглотителями атмосферного углерода, играют важную роль в сокращении выбросов CO2 и предотвращении потепления климата. Авторы попытались смоделировать биомассу модельных деревьев Quercus L.,используя данные 500 деревьев, распределенных вдоль транс-евразийских гидротермических градиентов. На сегодняшний день предложено несколько моделей биомассы деревьев и древостоев, включающих в качестве независимых переменных как их морфолого-структурные характеристики, так и климатические показатели. Существующие модели позволяют прогнозировать изменения биомассы вследствие сдвигов климатических трендов, но не показывают вклада климатических переменных в объяснение изменчивости биомассы, которая зависит как от вида дерева и древостоя, так и от структуры модели. Разработанные модели показывают, в какой степени отклонение от классической аллометрической модели, вызванное включением дополнительных независимых переменных, увеличивает вклад климатических переменных в объяснение изменчивости биомассы. Этот вклад наибольший, когда модель включает возраст, диаметр ствола, высоту дерева и их совокупный эффект. 3D-интерпретация«лучшей» модели показала пропеллеро-образную зависимость компонентов биомассы дуба от температуры и осадков, форма которой является зеркальным отражением аналогичной зависимости для биомассы деревьев двухвойных сосен и лиственниц. Это может быть связано с особенностями функционирования лиственных и хвойных видов. Forest ecosystems, as sinks of atmospheric carbon, play an important role in reducing CO2 emissions and preventing annual temperatures from rising. We attempted to model Quercus spp. single-tree biomass using the data from 500 sample trees distributed along the trans-Eurasian hydrothermal gradients. Today, several models of the biomass of trees and stands have been proposed, including both morphological-structural characteristics of trees and stands, and climate indicators as independent variables. The models make it possible to predict changes in biomass due to shifts in climate trends, but do not show the contribution of climate variables to the explanation of biomass variability, which depends on both the species of the tree and stand, and the structure of a model. The models designed show to what extent the deviation from the classical allometric model caused by the inclusion of additional independent variables, increases the contribution of climate variables to the explanation of biomass variability. The model shows the greatest contribution when itincludes age, stem diameter, tree height, and their combined effect. The 3D- interpretation of the «best» model showed a propeller-shaped dependence of the components of oak tree biomass on temperatures and precipitation, the shape of which is a mirror image of a similar dependence for the biomass of trees of two-needled pines and larches. This may be due to the functioning traits of leaved and coniferous species.

Drainage Network Patterns Determinism: A Comparison in Arid, Semi-Arid and Semi-Humid Area of Morocco Using Multifactorial Approach

Drainage network patterns influence the hydrological response of the watersheds and must be taken into account in the management of the water resource. In this context, it is important to identify the factors that control the configuration of drainage networks in and beyond specific climatic conditions. Here, we study 318 basins spread over three sectors (arid, semi-arid, and semi-humid) of Morocco where seven drainage network patterns have been identified. From each basin, 14 parameters were extracted, describing the relief, geology, morphometry, drainage network, land cover, precipitation, and time of concentration (Tc). Principal component analysis (PCA) and discriminant analysis (DA) processing were performed on the entire database and on each sector separately. The results show that the drainage network pattern is a feature of the landscape that contributes significantly to the variance of the basins. They suggest that the distribution of network patterns is controlled by the relationship between the different parameters, mainly those related to the relief, more than by the variations of each parameter taken individually. The network discrimination rate is 63.8%, which improves when each sector is treated separately. Confusion in discrimination are similar across all sectors and can be explained by similar conditions (active tectonic, deformation, and uplift) or transitions from one network pattern to another, due to the landscape evolution of certain sectors. A contribution of climatic variables appears locally but was attributed to a statistical coincidence, these parameters presenting a distribution close to that of the relief and geology variables.

Comprehensive analysis on the evolution characteristics and causes of river runoff and sediment load in a mountainous basin of China’s subtropical plateau

Under the background of climate variability and anthropogenic stresses, changes of the runoff and sediment processes have drawn increasing concerns during the past decades. Analyzing the evolution characteristics and causes of runoff and sediment load is critical for the sustainable development of water resource and terrestrial ecosystems of river basins. This study presents an integrated approach for analyzing the evolution characteristics of the annual runoff and sediment load, including the trend, periodicity, change point and their correlations in the Wujiang River basin (WRB) –a typical mountainous river system in southwest China, based on the observed data during the period 1970–2016. On this basis, the contributions of climate variability and human activities on runoff change were first distinguished by using a widely applied Budyko-based hydrological sensitivity method, and then the quantified result was further applied in the attribution analysis of river sediment load change. Research results revealed that the change patterns of runoff and sediment processes, such as the trend, periodicity and potential change point, as well as the relationships of precipitation-runoff and runoff-sediment load are quite different in the WRB. Quantitative assessment revealed that climate variability contributes to 71.5%–85.6% changes of mean annual runoff in 1985–1994, 1995–2004 and 2005–2016 with reference to the baseline period of 1970–1984. In contrary, human activities dominate the reduction of sediment load in the river, and the contribution rate ranged in 67.2%–107.5%. Variations of annual runoff in the WRB was the direct result of climate variability, while land use change played a secondary role. The construction of cascade hydropower reservoirs, particularly in the upper and middle reaches of the Wujiang River is fundamentally responsible for the significant decreasing and the weakened periodicity of sediment load as well as the changed runoff-sediment load correlation at Wulong station in recent years. However, this influence was not big enough to modify the regime of annual runoff.

Conservation planning of cash crops species (Garcinia gummi-gutta) under current and future climate in the Western Ghats, India

Agriculture, global biodiversity and distribution of species are increasingly influenced by changing climate. Assessing the future distribution of biodiversity under different climate change scenarios is an essential step towards conservation planning and policy implementations. To understand the climate change impacts, the present study used Garcinia gummi-gutta cash crop species as a case study that is even exported, adding the nation’s foreign reserve. Given the importance of this crop for local and national economy, the main objectives of the study were to analyse the impact of present and future climates on ecologically susceptible G. gummi-gutta species in the Western Ghats based on maximum entropy model (MaxEnt). Future projections with RCP scenarios for 2050 and 2070 were made using the data of 84 species occurrence and climatic variables of three climate models from IPCC 5th assessment. The contribution of climatic variables was analysed by jackknife test, and 0.888 of AOC indicates high accuracy of the model results. It was found that annual precipitation, coldest quarter precipitation, and precipitation seasonality were the key determining factors for the suitability of this species. In addition, the results of all scenarios showed that the current suitability of the species would be dramatically decreased by 2050 and 2070. The study suggests how the MaxEnt approach can be an important tool for agricultural development, management of species habitats, conservation of biodiversity, and climate change rehabitation planning.

Partitioning the impacts of land use/land cover change and climate variability on water supply over the source region of the Blue Nile Basin

AbstractWater plays a vital role in sustaining the natural functioning of the entire ecosystem that supports life on Earth. It plays key roles in the well‐being of society in numerous ways. However, climate variability and land use land cover (LULC) change have caused spatiotemporal water supply variation. Disentangling the effects of climate variability from LULC change on water supply is crucial for sustainable water resource management. The main purpose of this study is, therefore, to disentangle the relative contribution of LULC change and climate variability to the overall average annual water supply variation. Residual trends analysis combined with Integrated Valuation of Environmental Services and Tradeoffs (InVEST) annual water yield model was adopted to perform simulations and disentangle the relative impacts of climate variability and LULC change. Ground and satellite data were used in this study. The study area has experienced a significant increasing wetness trend and significant LULC dynamics between 2003 and 2017. As a result, an increasing water supply was observed due to the joint effects of climate variability and LULC change in the watershed (203 mm). The contribution of climate variability was 94%, whereas LULC contributes only 6% from 2003 to 2017. Climate variability negatively led to water supply variation while LULC change contributed positively from 2010 to 2017. Although the ongoing soil and water conservation (SWC) practices improved vegetation cover and water retention of the watershed, climate variability is the main driver of water supply variation. Therefore, SWC practices should incorporate ecosystem‐based climate change adaptation strategies and scale up to community‐based integrated watershed management to sustain water supply.

Climate change and finger millet: Perception, trend and impact on yield in different ecological regions in Central Nepal

The views of local people on climate change along different ecological regions are relatively unexplored in Nepal. This study was conducted in 13 villages in central Nepal at different altitudes to document the views of small holder farmers and compare their perception with trends of climatic variables, finger millet yield, natural disasters, plant phenology (flowering and fruiting), status of forest and wild life, as well as the spread of diseases and pests. Analysis on the climatic data of stations for 36–41 years between 1975 and 2016 showed significant increases in the minimum temperature in lower tropical climatic region (<500 m), upper tropical to subtropical climatic region (500–2000 m) and temperate climatic region (2000–3000 m) by 0.01, 0.026 and 0.054°C/year, respectively, and an increase of maximum temperature by 0.008, 0.018, and 0.019°C/year, respectively. Rainfall showed a strongly significant decreasing trend in all elevation regions. This result matches with the views of respondents except 38% respondent from temperate climatic region. People from the temperate climatic region also mentioned that current onset of snowfall is delayed but amount of snowfall remained the same. From the documented records, except events of wild fire, frequency of natural disasters events have increased in the recent years, which was in harmony with the views of local people. Multi-linear regression analysis showed that contribution of climatic variables on finger millet yield in lower tropical climatic region and upper tropical to subtropical regions was 23% and 57.3%, respectively, which was supported by increasing trend on average growing degree day (GDD) temperature at the rate of 0.01°C in upper tropical to subtropical region and 0.007°C in lower tropical climatic region yearly. Finger millet yield has been increasing at the rate of 7.39 and 36.9 kg/ha yearly in lower tropical climatic region and upper tropical to subtropical climatic region, respectively. This result provides deeper understanding of people’s perception of causes and effects of climate change on diverse variables along different elevation and related magnitude which can contribute to policy making in Nepal.

Water level variation characteristics under the impacts of extreme drought and the operation of the Three Gorges Dam

Under the influence of a climate of extreme drought and the Three Gorges Dam (TGD) operation, the water levels in the middle and lower reaches of the Yangtze River in 2006 and 2011 changed significantly compared with those in the extreme drought years of 1978 and 1986. To quantitatively analyze the characteristics of water level variations in 2006 and 2011, a new calculation method was proposed, and the daily water level and discharge from 1955–2016 were collected in this study. The findings are as follows: in 2006 and 2011, the water level in the dry season significantly increased, but that in the flood season obviously decreased compared with the levels in 1978 and 1986. Here, we described this phenomenon as “no low-water-level in dry season, no high-water-level in flood season”. Based on the calculation method, the contributions of climate variability and the Three Gorges Dam operation to water level variations in the middle and lower reaches of the Yangtze River were calculated, and the contributions indicated that climate variability was the main reason for the phenomenon of “no low-water-level in dry season, no high-water-level in flood season” instead of flood peak reduction in the flood season and drought runoff implementation in the dry season, which are both induced by TGD.

Using the Mann–Kendall test and double mass curve method to explore stream flow changes in response to climate and human activities

AbstractAnalyzing intra-annual stream flow can reveal the main causes for runoff changes and the contributions of climate variability and human activities. For this purpose, the Mann–Kendall and cumulative rank difference (CRD) tests, and the double mass curve method, were applied to a time series of hydro-meteorological variables from 1971 to 2010 in the Tajan River basin in Iran. Results indicated that runoff changes in the wet and dry seasons after 1999 had significant respective decreasing and increasing trends, at the 0.01 confidence level, due to dam construction. In the pre-dam period (1991–1998), the results of the double mass curve method showed that climate variability and human activities contributed 57.76% and 42.24%, respectively, to the runoff decrease during the wet season. For the post-dam period (1999–2010), climate variability and anthropogenic activities contributed 24.68% and 75.32%, respectively, to the wet season runoff decrease of 116.55 mm. On the other hand, in the same period during the dry season, climate variability contributed −30.68% and human activities contributed 130.68% to the runoff increase of 41.45 mm. It is evident that runoff changes in both wet and dry seasons were mainly due to human activities associated with dam construction to meet water supply demands for agriculture.

SWAT-Simulated Streamflow Responses to Climate Variability and Human Activities in the Miyun Reservoir Basin by Considering Streamflow Components

The streamflow into Miyun Reservoir, the only surface drinking water source for Beijing City, has declined dramatically over the past five decades. Thus, the impacts of climate variability and human activities (direct and indirect human activities) on streamflow and its components (baseflow and quickflow) needs to be quantitatively estimated for the sustainability of regional water resources management. Based on a heuristic segmentation algorithm, the chosen study period (1969–2012) was segmented into three subseries: a baseline period (1969–1979) and two impact periods I (1980–1998) and II (1999–2012). The Soil and Water Assessment Tool (SWAT) was adopted to investigate the attributions for streamflow change. Our results indicated that the baseflow accounted for almost 63.5% of the annual streamflow based on baseflow separation. The contributions of climate variability and human activities to streamflow decrease varied with different stages. During impact period I, human activities was accountable for 54.3% of the streamflow decrease. In impact period II, climate variability was responsible for 64.9%, and about 8.3 mm of baseflow was extracted from the stream on average based on the comparison of the observed streamflow and simulated baseflow. The results in this study could provide necessary information for water resources management in the watershed.

Influence of climate variability and human activities on stream flow variation in the past 50 years in Taoer River, Northeast China

Taoer River Basin, which is located in the west of Northeast China, is an agropastoral ecotone. In recent years, the hydrological cycle and water resources have changed significantly with the deterioration of the environment. Many water problems such as river blanking, wetland shrinking and salinization have occurred in this region. All of these phenomena were directly caused by changes in stream flow under climate variability and human activities. In light of the situation, the impact of climate variability and human activities on stream flow should be identified immediately to identify the primary driving factors of basin hydrological processes. To achieve this, statistical tests were applied to identify trends in variation and catastrophe points in mean annual stream flow from 1961 to 2011. A runoff sensitive coefficients method and a SIMHYD model were applied to assess the impacts of stream flow variation. The following conclusions were found: 1) The years 1985 and 2000 were confirmed to be catastrophe points in the stream flow series. Thus, the study period could be divided into three periods, from 1961 to 1985 (Period I), 1986 to 2000 (Period II) and 2001 to 2011 (Period III). 2) Mean annual observed stream flow was 31.54 mm in Period I, then increased to 65.60 mm in Period II and decreased to 2.92 mm in Period III. 3) Using runoff sensitive coefficients, the contribution of climate variability was 41.93% and 43.14% of the increase in stream flow during Periods II and III, suggesting that the contribution of human activities to the increase was 58.07% and 56.86%, respectively. 4) Climate variability accounted for 42.57% and 44.30% of the decrease in stream flow, while human activities accounted for 57.43% and 55.70% of the decrease, according to the SIMHYD model. 5) In comparison of these two methods, the primary driving factors of stream flow variation could be considered to be human activities, which contributed about 15% more than climate variability. It is hoped that these conclusions will benefit future regional planning and sustainable development.

Impact on Water Quality of Nandoni Water Reservoir Downstream of Municipal Sewage Plants in Vhembe District, South Africa

The deterioration of water quality in our freshwater sources is on the increase worldwide and, in South Africa, mostly due to the discharge of municipal sewage effluent. Here we report on the use of principal component analysis, coupled with factor and cluster analysis, to study the similarities and differences between upstream and downstream sampling sites that are downstream of municipal sewage plants. The contribution of climatic variables, air temperature, humidity, and rainfall were also evaluated with respect to variations in water quality at the sampling sites. The physicochemical and microbial values were higher than the Department of Water Affairs and Forestry (DWAF) and World Health Organization (WHO) guidelines. The cluster analysis showed the presence of two clusters for each of the Mvudi, Dzindi, and Luvuvhu Rivers and Nandoni reservoir sampling sites. The principal component analysis (PCA) accounted for 40% of the water quality variation and was associated strongly with pH, electrical conductivity, calcium, magnesium, chloride, bromide, nitrate, and total coliform, and negatively with rainfall, which represented Mvudi downstream and was attributed to the Thohoyandou sewage plant. The PCA accounted for 54% of the variation and was associated strongly with electrical conductivity, sulfate; total dissolved solids, fluoride, turbidity, nitrate, manganese, alkalinity, magnesium, and total coliform represented Dzindi downstream, with inflows from the Vuwani sewage plant and agriculture. The PCA accounted for 30% of the variation and was associated strongly with total dissolved solids, electrical conductivity, magnesium, fluoride, nitrate, sulfate, total coliform average air temperature, and total rainfall, and negatively associated with manganese and bromide represented Luvuvhu upstream and was associated with commercial agriculture. The PCA accounted for 21% of the variation and was associated strongly with turbidity, alkalinity, magnesium, chloride, fluoride, nitrate, and strongly negatively associated with rainfall, which represented Luvuvhu downstream, associated with inflows from Vuwani oxidation ponds, Elim and Waterval sewage plants, and agriculture. The PCA accounted for 14% of the variation and was moderately associated with rainfall and weakly associated with chloride and bromide and negatively associated with nitrate, which represented the natural Nandoni reservoir system. The continued discharge of effluent may render the raw water supply unsuitable for human consumption and lead to eutrophication due to nitrate enrichment and proliferation of harmful algal blooms and schistomiasis infections in the long term.

Contributions of climate variability and human activities to the variation of runoff in the Wei River Basin, China

ABSTRACTThe Wei River Basin is a typical arid and semi-arid area of the Yellow River Basin. Quantitative estimates of the contributions of human activities and climate changes in this region will enhance our understanding of the local hydrological mechanism and provide an effective reference for other arid and semi-arid areas of the world in local water resource planning and management. The heuristic segmentation method was used to detect the inflection points of the annual runoff. The slope change ratio of accumulative quantity (SCRAQ) method was applied to compute the relative contributions of human activities and climate changes to the decreasing runoff in the whole basin and the basin above Linjiacun. For the whole basin, when 1960–1969 is selected as the baseline, the contributions of climate changes and human activities in 1970–1993 are 26.47% and 73.53%, respectively, those in 1993–2005 are 23.33% and 76.67%, respectively. When 1970–1993 is selected as the baseline, the contributions of climate and human impacts in 1994–2005 are 18.88% and 81.12%, respectively. The results imply that human activities are the dominant driving factors of runoff reduction, whose effect is increasingly intensifying. Furthermore, in order to verify the contributions of human activities and climate changes based on the SCRAQ method, an approach based on the Budyko hypothesis was used in this paper. The results indicate that the contributions of human activities and climate changes based on the SCRAQ method are consistent with those based on the sensitivity-based method.Editor Z.W. Kundzewicz; Associate editor D. Yang

Relative contribution of land use change and climate variability on discharge of upper Mara River, Kenya

Abstract Study region Nyangores River watershed, headwater catchment of Mara River basin in Kenya. Study focus Climate variability and human activities are the main drivers of change of watershed hydrology. The contribution of climate variability and land use change to change in streamflow of Nyangores River, was investigated. Mann Kendall and sequential Mann Kendall tests were used to investigate the presence and breakpoint of a trend in discharge data (1965–2007) respectively. The Budyko framework was used to separate the respective contribution of drivers to change in discharge. Future response of the watershed to climate change was predicted using the runoff sensitivity equation developed. New hydrological insights for the region There was a significant increasing trend in the discharge with a breakpoint in 1977. Land use change was found to be the main driver of change in discharge accounting for 97.5% of the change. Climate variability only caused a net increase of the remaining 2.5% of the change; which was caused by counter impacts on discharge of increase in rainfall (increased discharge by 24%) and increase in potential evapotranspiration (decreased discharge by 21.5%). Climate change was predicted to cause a moderate 16% and 15% increase in streamflow in the next 20 and 50 years respectively. Change in discharge was specifically attributed to deforestation at the headwaters of the watershed.