Impact Of Precipitation Variability Research Articles

Precipitation changes and their relationships with vegetation responses during 1982–2015 in Kunhar River basin, Pakistan

AbstractPrecipitation is a major determinant of vegetation growth. The impact of precipitation variability is more pronounced in ecosystems where sensitive vegetation is apparent. Therefore, understanding the relationship between precipitation and vegetation is vital to guide appropriate measures towards fragile biomes. We investigated the trends and correlations between precipitation and normalized difference vegetation index (NDVI) for 1982–2015 over the Kunhar River basin, Pakistan, using satellite-derived NDVI and globally available interpolated precipitation datasets. Subsequently, we attempt to identify vegetation types that are influenced by precipitation changes. Results show a general decreasing trend in vegetation activity as we go from southern to northern portions of the basin. This decrease is also accompanied by the similarly decreasing precipitation trend in the same direction. The similarity of spatial patterns between the two variables can indicate that, in general, precipitation is playing a guiding role in determining vegetation distribution in the basin. Our lagged correlation analysis revealed that strong precipitation–vegetation correlations (r > 0.75) are rare in the basin. Agricultural and forested areas show moderate correlations (0.5 < r < 0.75) when NDVI is correlated with the previous month's precipitation values (lag1). In simultaneous month correlation (lag0) and the rest of the lagged correlations (lag2 and lag3), a weak association between precipitation and NDVI is observed. The moderate and weak correlations over the basin might indicate that precipitation is not the only factor influencing vegetation growth in the Kunhar River basin. Other climatic and biogeographic factors such as temperature, solar radiation, topography and soil characteristics also play additional roles in vegetation activities. The results can provide a technical basis and valuable reference to ecological management strategies in the Kunhar River basin for concerned decision-makers and stakeholders.

An approach to simulate the climate-driven streamflow in the data-scarce mountain basins of Northwest China

With global warming, the inland river basin in the arid region of Northwest China is facing a serious water supply situation. The headwater basin of the inland river is located in the high-altitude mountainous region, and there are few meteorological observation sites, so it is difficult to apply distributed hydrological models and other models based on the physical mechanism of runoff generation to evaluate climate change and its impact on streamflow. To simulate the climate-driven streamflow in data-scarce mountain basins of Northwest China, we developed an integrated approach by using downscaled reanalysis data, Mann–Kendall test, ensemble empirical mode decomposition and backpropagation artificial neural networks together with the weights connection method. We validated the approach in the Kaidu River basin located in the Tianshan mountains. The results showed that the streamflow increased 12.9% by $$2.5 \times 10^{8}\,\hbox {m}^{3}$$ per decade with the warm and wet climate, while the average annual temperature increased 5.2% at a rate of $$0.3{^{\circ }}\hbox {C}$$ per decade and the precipitation increased 37.3% at a rate of 16.4 mm per decade during the period from 1980 to 2015. The impact of temperature variability on streamflow was 44.21 ± 2.08% and the impact of precipitation variability on streamflow was 55.79 ± 2.08%.

Impact of precipitation variability on the performance of a rainfall–runoff model in Mediterranean mountain catchments

ABSTRACTLosses in performance of a low-dimensional rainfall–runoff model resulting from changes in the annual precipitation are assessed for five catchments located in a mountainous Mediterranean environment, the Troodos Mountains, Cyprus. For an increase of 25% or a decrease of 15% in the cumulative precipitation depth of a five-year period, model performance losses become significant: the model robustness criterion reaches 13% and simulated cumulative runoff is under- or overestimated by up to 20%. However, only the 25% decrease in the precipitation depth influences the ability of the model to predict runoff dynamics (10% decrease in the Nash-Sutcliffe coefficient). This indicates the occurrence of either non-stationary effects or temporary secondary hydrological processes, which tend to amplify the decrease (or increase) in runoff production during the drier (or wetter) period. In addition, losses in model performance are analysed between one catchment and another. High performance losses despite close physical catchment properties show the poor transferability of model parameters in this environment.Editor D. Koutsoyiannis; Associate editor Y. Gyasi-Agyei

Impacts of precipitation variability on plant species and community water stress in a temperate deciduous forest in the central US

Variations in precipitation regimes can shift ecosystem structure and function by altering frequency, severity and timing of plant water stress. There is a need for predictively understanding impacts of precipitation regimes on plant water stress in relation to species water use strategies. Here we first formulated two complementary, physiologically-linked measures of precipitation variability (PV)—Precipitation Variability Index (PVI) and Average Recurrence Interval of Effective Precipitation (ARIEP). We then used nine-year continuous measurements of Predawn Leaf Water Potential Integral (PLWPI) in a central US forest to relate PVI and ARIEP to actual plant water availability and comparative water stress responses of six species with different capacities to regulate their internal water status. We found that PVI and ARIEP explained nearly all inter-annual variations in PLWPI for all species as well as for the community scaled from species measurements. The six species investigated showed differential sensitivities to variations in precipitation regimes. Their sensitivities were reflected more in the responses to PVI and ARIEP than to the mean precipitation rate. Further, they exhibited tradeoffs between responses to low and high PV. Finally, PVI and ARIEP were closely correlated with temporal integrals of positive temperature anomalies and vapor pressure deficit. We suggest that the comparative responses of plant species to PV are part of species-specific water use strategies in a plant community facing the uncertainty of fluctuating precipitation regimes. PVI and ARIEP should be adopted as key indices to quantify physiological drought and the ecological impacts of precipitation regimes in a changing climate.

HyMeX: A 10-Year Multidisciplinary Program on the Mediterranean Water Cycle

The Mediterranean countries are experiencing important challenges related to the water cycle, including water shortages and floods, extreme winds, and ice/snow storms, that impact critically the socioeconomic vitality in the area (causing damage to property, threatening lives, affecting the energy and transportation sectors, etc.). There are gaps in our understanding of the Mediterranean water cycle and its dynamics that include the variability of the Mediterranean Sea water budget and its feedback on the variability of the continental precipitation through air–sea interactions, the impact of precipitation variability on aquifer recharge, river discharge, and soil water content and vegetation characteristics specific to the Mediterranean basin and the mechanisms that control the location and intensity of heavy precipitating systems that often produce floods. The Hydrological Cycle in Mediterranean Experiment (HyMeX) program is a 10-yr concerted experimental effort at the international level that aims to advance the scientific knowledge of the water cycle variability in all compartments (land, sea, and atmosphere) and at various time and spatial scales. It also aims to improve the processes-based models needed for forecasting hydrometeorological extremes and the models of the regional climate system for predicting regional climate variability and evolution. Finally, it aims to assess the social and economic vulnerability to hydrometeorological natural hazards in the Mediterranean and the adaptation capacity of the territories and populations therein to provide support to policy makers to cope with water-related problems under the influence of climate change, by linking scientific outcomes with related policy requirements.

River flow trends in the west of Iran during the past 40 years: Impact of precipitation variability

A better understanding of hydrological changes associated with climate change can be achieved by analyzing the temporal trends in river discharge time series. We used the non-parametric Spearman's rho, Kendall's tau, Mann–Kendall and Theil–Sen approaches to evaluate annual and monthly trends in river flow data from 12 stations located in the mountainous western regions of Iran over a 40-year period spanning the hydrological years 1969–1970 to 2008–2009. The Pearson correlation analysis was also applied to explore the relationships between precipitation and river flow series. Using a 5% significance level, we found an evidence of downward trends in annual river discharge at Varayeneh, Omar-Abad, Saleh-Abad, Zehtaran and Bahadorbeig stations at the rates of 0.491, 1.00, 0.101, 0.044, and 0.020m3/s per decade, respectively. These significant downward trends started in the hydrological years of 2005–2006, 2000–2001, 2006–2007, 1995–1996 and 1995–1996, respectively. The greatest numbers of stations with significant river discharge trends occur in October and November, accounting for seven and six stations respectively. Annual precipitation exhibited no strong directional trend, although the tendency was toward increasing annual precipitation. Monthly precipitation variability seems to be also increasing for most of the months but no overall trend pattern in monthly precipitation totals emerged. Correlation analyses indicated strong relationships between river discharge and precipitation at the annual scale and for most of the months.

Hydrologic variability and its influence on long‐term peat dynamics

Peatlands are carbon‐rich ecosystems that are extensive in the northern high latitudes where significant 21st century climate changes are expected. In response to climate change, peatlands may become a net source of greenhouse gases, thereby inducing a positive climate feedback effect. In this paper, the impact of precipitation variability and the mean climate state on long‐term peat accumulation is investigated with model simulations. The models couple peat accumulation with the hydrological cycle, which results in peatland bistability, where peatlands may take the physical characteristics from one of two possible alternative stable states. The models consider precipitation as a stochastic forcing variable, temperature‐dependent functions and are parameterized with climatology and peat characteristics to represent the West Siberian Lowlands (WSL) between 55°N and 60°N. Observed WSL peat depths statistically imply bistability. Peatland bistability, however, is eliminated in model simulations with moderate‐to‐large precipitation variability and warmer and wetter climates. This suggests that projected late 21st century climate change would put the thick peatlands in WSL on a transition to thin peatlands. The loss of thick peatlands could significantly increase atmospheric carbon dioxide and provide a positive climate feedback effect. However, the impacts depend on the importance of unaccounted stabilizing factors. The study also shows that precipitation variability induces peatlands to switch between extended periods of accumulation and depletion even if the peatlands are in long‐term equilibrium. Thus, short‐term observations may see only natural fluctuations and new, longer‐term observational strategies are necessary to diagnose if peatlands are undergoing fundamental changes.

The impact of altered precipitation variability on annual weed species

Climate change models predict increasing variability in precipitation across the globe, with an increase in the incidence of large precipitation events but decreasing overall event frequency. Research with annual species in arid and semiarid ecosystems has demonstrated that precipitation variability can influence plant community dynamics; however, less is known about the impact of precipitation variability in less water-limited ecosystems, including economically important agricultural systems. • We conducted three greenhouse experiments to determine how variation in total precipitation and the interval between precipitation events affected emergence and growth of two common annual midwestern weed species, Chenopodium album (Chenopodiaceae) and Setaria faberi (Poaceae). • Both species responded to precipitation variability; however, the effect depended on life stage and precipitation amount, indicating that responses are highly context-dependent. Emergence of both species increased with longer intervals between precipitation events at low total precipitation, but species' responses varied under typical precipitation amounts. Individual seedling biomass of both species depended on interactions between total water and intervals, but species' responses differed; Setaria faberi biomass was reduced with longer intervals, but Chenopodium album had either a positive or no response. • Our results suggest that changes in precipitation variability likely will affect the composition and relative abundance of agriculturally important weeds. These results are important for understanding how changes in the temporal variability of precipitation due to global climate changes could impact plants in non-arid communities.

Using climate information for supporting climate change adaptation in water resource management in South Africa

Water resources, and in particular run-off, are significantly affected by climate variability. At present, there are few examples of how the water management sector integrates information about changing intra-annual climate conditions in a systematic manner in developing countries. This paper, using the case study of Cape Town in the Western Cape, South Africa, identifies processes and products to facilitate increased uptake of seasonal climate forecasts among water resource managers. Results suggest that existing seasonal forecasts do not focus enough on specific users’ needs. In order to increase uptake, forecasts need to include information on the likely impact of precipitation variability on runoff and water availability. More opportunities are also needed for those with climate knowledge to interact with water resource managers, particularly in the developing country context where municipal managers’ capacity is strained. Although there are challenges that need to be overcome in using probabilistic climate information, seasonal forecast information tailored to the needs of water resource planners has the potential to support annual planning and is therefore a means of adapting to climate change.

Issues in model validation: assessing the performance of a regional-scale acid deposition model using measured and modelled data

The development and validation of a new version of the Hull Acid Rain Model (HARM12.1) is described in the context of changes in emissions and deposition estimates supplied by the Centre for Ecology and Hydrology (CEH) Edinburgh based on the available measurement networks. Major changes to the model include greater vertical resolution, the adoption of new background concentrations and ecosystem-specific deposition velocities. HARM output for 1998–2000 is compared with data from the rural SO 2 , NO 2 and NH 3 networks and results from the nitric acid and aerosol network. The ability to reproduce deposition estimates based on measurements is key to a regional-scale model like HARM. Changes in these estimates between 1995–97 and 1998–2000 are discussed. Comparing HARM modelled deposition and the CEH data indicates that the new version of the model performs better in this respect than its predecessor (HARM11.5). The trend in deposition over the time period does not seem to reflect the marked reduction in emissions. The possible reasons for this are explored with particular emphasis on changes in precipitation. 1995–97 was unusually dry, while 1998–2000 was wet. Changes in rainfall concentration and unmodified deposition are presented for comparison with HARM and CEH estimates. It is clear that the impact of precipitation variability on modelled acid deposition requires further investigation. Finally, we compare HARM12.1 and HARM 11.5 deposition in 2010 following emissions reductions to meet the terms of the National Emissions Ceilings Directive.