Decrease In Annual Precipitation Research Articles

Modeling climate change impacts on precipitation in arid regions of Pakistan: a non-local model output statistics downscaling approach

The uncertainties in climate projections in arid regions are quite high due to the large variability of climate and the lack of high-quality climate observations. In this study, an ensemble of four Coupled Model Intercomparison Project Phase 5 (CMIP5) General Circulation Model (GCM) namely GISS-E2-H, HadGEM2-ES, MIROC5, and NorESM1-M simulations was downscaled for the assessment of the spatiotemporal changes in precipitation in the data-scarce arid province (Balochistan) of Pakistan for four Representative Concentration Pathway (RCP) scenarios. The gauge-based gridded precipitation data of the Global Precipitation Climatology Centre (GPCC) having a spatial resolution of 0.5° was used for this purpose. Support Vector Machine (SVM) was used for the development of non-local model output statistics (MOS) downscaling models for each grid by linking the GPCC precipitation with the GCM simulated precipitation across a spatial domain (latitudes 03°–45° N and longitudes 42°–92° E). Then, Random Forest (RF) algorithm was used to develop the multi-model ensemble (MME) of downscaled precipitation projections. The performances of the models were assessed in terms of normalized root mean square error (NRMSE), percentage of bias (PBIAS), and modified index of agreement (md). The results indicated that the non-local SVM-based MOS models coupled with RF MME can simulate historical precipitation over the region quite well. The MME of GCMs projected changes in the annual, monsoon, and winter precipitation in the range of − 30% to 30% for different RCPs. Overall, the MME of GCMs indicated an increase in precipitation in the monsoon-dominated wetter regions in the east, while a decrease in winter precipitation dominated arid region in the west. A decrease in annual precipitation over the majority of the southeast, east, and northeastern arid regions was projected which may increase the aridity in the region.

Effect of Climate Change on Soil Erosion in a Mountainous Mediterranean Catchment (Central Pindus, Greece)

The aim of this study was to assess soil erosion changes in the mountainous catchment of the Portaikos torrent (Central Greece) under climate change. To this end, precipitation and temperature data were derived from a high-resolution (25 × 25 km) RegCM3 regional climate model for the baseline period 1974–2000 and future period 2074–2100. Additionally, three GIS layers were generated regarding land cover, geology, and slopes in the study area, whereas erosion state was recognized after field observations. Subsequently, the erosion potential model (EPM) was applied to quantify the effects of precipitation and temperature changes on soil erosion. The results showed a decrease (−21.2%) in annual precipitation (mm) and increase (+3.6 °C) in mean annual temperature until the end of the 21st century, and the above changes are likely to lead to a small decrease (−4.9%) in soil erosion potential.

Formation of a Rain Shadow: O and H Stable Isotope Records in Authigenic Clays From the Siwalik Group in Eastern Bhutan

AbstractWe measure the oxygen and hydrogen stable isotope composition of authigenic clays from Himalayan foreland sediments (Siwalik Group), and from present day small stream waters in eastern Bhutan to explore the impact of uplift of the Shillong Plateau on rain shadow formation over the Himalayan foothills. Stable isotope data from authigenic clay minerals (<2 μm) suggest the presence of three paleoclimatic periods during deposition of the Siwalik Group, between ∼7 and ∼1 Ma. The mean δ18O value in paleometeoric waters, which were in equilibrium with clay minerals, is ∼2.5‰ lower than in modern meteoric and stream waters at the elevation of the foreland basin. We discuss the factors that could have changed the isotopic composition of water over time and we conclude that (a) the most likely and significant cause for the increase in meteoric water δ18O values over time is the “amount effect,” specifically, a decrease in mean annual precipitation. (b) The change in mean annual precipitation over the foreland basin and foothills of the Himalaya is the result of orographic effect caused by the Shillong Plateau's uplift. The critical elevation of the Shillong Plateau required to induce significant orographic precipitation was attained after ∼1.2 Ma. (c) By applying scale analysis, we estimate that the mean annual precipitation over the foreland basin of the eastern Bhutan Himalayas has decreased by a factor of 1.7–2.5 over the last 1–3 million years.

Hydrological Modeling of Climate Change Impacts in a Tropical River Basin: A Case Study of the Cauto River, Cuba

The soil and water assessment tool (SWAT) model was applied for the first time in Cuba to assess the potential impacts of climate change on water availability in the Cauto River basin. The model was calibrated (and validated) for the 2001–2006 (2007–2010) period at a monthly timescale in two subbasins La Fuente and Las Coloradas, representative of middle and upper sections of the Cauto basin; the calibrated models showed good performance. The output available for the regional climate Model RegCM4.3 was used to force the calibrated SWAT models to simulate a baseline (1970–2000) period and near-future (2015–2039) hydrologic regimes under the representative concentration pathway (RCP) 8.5 emission scenario. The future projections suggest regional increases of 1.5 °C in mean annual temperature and a 38% decrease in mean annual precipitation in the subbasins. These changes translate to possible reductions in the annual streamflow of up to 61% with respect to the baseline period, whereas the aquifer recharge in the basin is expected to decrease up to 58%, with a consequent reduction of groundwater flow, especially during the boreal summer wet season. These projection scenarios should be of interest to water resources managers in tropical regions.

Climatic variability over the 20th century and future drift during wheat (Triticum aestivum) growing period in Uttarakhand region, India

An effort was made to analyze the spatial and temporal variability of rainfall and temperature in 13 districts of the Uttarakhand, India over the period of 102 years (1901–2002). The main focus was to examine the rainfall variability and its future response during wheat crop period (November-April). Mann–Kendall test and Sen's slope estimator test used to detect monotonic trend direction and magnitude of change over time on annual and seasonal basis. The Pettit-Mann–Whitney test applied to detect the change points over the century. Mean annual precipitation varied from 821 mm (in Haridwar) to 1244 mm (in Pithoragarh) whereas it was 75 mm (in Udham Singh Nagar) to 178 mm (in Pithoragarh) during wheat growing period. During the wheat crop period, annual precipitation decrease was noticed in Udham Singh Nagar (-37.1%) which was maximum. Maximum decrease in minimum and maximum temperature during wheat growing period and annual period was observed for Uttarkashi district which was -39.4%, -28% and -25.1%, -21.1%, respectively. Similarly, Champawat was second after Udham Singh Nagar having highest temperature in both the periods. The most affected year of change was 1978 and 1940 in annual precipitation and maximum, minimum temperature, but during wheat growing period it was observed in 1945 and 1978, respectively. Mann Kendal trend test shows decrease in precipitation for all the stations during wheat growing period and annual period. In case of annual minimum temperature, average change was 0.0040C, though during wheat crop period it was 0.009 0C /year.

Increasing Flash Floods in a Drying Climate over Southwest China

In a globally warming world, subtropical regions are generally expected to become drier while the tropics and mid–high latitudes become wetter. In line with this, Southwest China, close to 25°N, is expected to become increasingly prone to drought if annual mean precipitation decreases. However, despite this trend, changes in the temporal distribution of moisture supply might actually result in increased extreme rainfall in the region, whose climate is characterized by distinct dry and wet seasons. Using hourly and daily gauge observations, rainfall intensity changes since 1971 are examined for a network of 142 locations in the region. From the analysis, dry season changes are negligible but wet season changes exhibit a significantly strong downward trend [−2.4% (10 yr)−1], particularly during the past 15 years [−17.7% (10 yr)−1]. However, the intensity of events during the wettest of 5% hours appears to steadily increase during the whole period [1.4% (10 yr)−1], tying in with government statistical reports of recent droughts and flooding. If the opposing trends are a consequence of a warming climate, it is reasonable to expect the contradictory trend to continue with an enhanced risk of flash flooding in coming decades in the region concerned.

Analysis of precipitation characteristics on the loess plateau between 1965 and 2014, based on high-density gauge observations

The Loess Plateau is ecologically vulnerable and one of the most severely eroded areas in China. In this study, we used daily precipitation data from 170 meteorological stations for the period 1965 to 2014 to systematically analyze the spatiotemporal variability of annual precipitation on the plateau, and to determine the dominant factors influencing changes in annual precipitation. The average annual precipitation is between 400 mm and 600 mm in most regions of the plateau, and precipitation is concentrated in the summer months (June to August). The greatest precipitation is in the southeastern region, but the amount has declined over the past 50 years. Morever, there have been decreases in extreme precipitation events in the southeastern region, and only minor changes in the continuous drought. Erosive rainfall is closely related to the total annual precipitation across the Loess Plateau region, and has decreased along with the decreases in annual precipitation, especially in the southeastern region. Changes in erosive rainfall account for >80% of interannual precipitation variability over large areas of the Loess Plateau. The variability in annual precipitation on the plateau is mainly affected by changes in the intensity and frequency of precipitation; changes in the length of the rainy season have only a minimal effect. Precipitation frequency contributes about 30% to interannual precipitation variability across the region as a whole. However, the eastern region is predominantly affected by changes in precipitation intensity, which contributes about 70% of the variability. These results provide valuable information to determine the dominant factor(s) influencing annual precipitation on the Loess Plateau, and may also be useful in the prevention and control of drought and soil erosion on the plateau.

Modelling the potential impacts of afforestation on extreme precipitation over West Africa

This study examines how afforestation in West Africa could influence extreme precipitation over the region, with a focus on widespread extreme rainfall events (WEREs) over the afforestation area. Two regional climate models (RegCM and WRF) were applied to simulate the present-day climate (1971–2000) and future climate (2031–2060, under IPCC RCP 4.5 emission scenario) with and without afforestation of the Savannah zone in West Africa. The models give a realistic simulation of precipitation indices and WEREs over the subcontinent. On average, the regional models projected future decreases in total annual wet day precipitation (PRCPTOT) and total annual daily precipitation greater than or equal to the 95th percentile of daily precipitation threshold (R95pTOT) and increases in maximum number of consecutive dry days (CDD) over Sahel. Over Savannah, the models projected decreases in PRCPTOT but increases in R95pTOT and CDD. Also, an increase in WEREs frequency is projected over west, central and east Savannah, except that RegCM simulated a decrease in WEREs over east Savannah. In general, afforestation increases PRCPTOT and R95pTOT but decreases CDD over the afforestation area. The forest-induced increases in PRCPTOT and decreases in CDD affect all ecological zones in West Africa. However, the simulations show that afforestation of Savannah also decreases R95pTOT over the Guinea Coast. It further increases WEREs over west and central Savannah and decreases them over east Savannah because of the local decrease in R95pTOT. Results of this study suggest that the future changes in characteristics of extreme precipitation events over West Africa are sensitive to the ongoing land modification.

A Ricardian valuation of the impact of climate change on Nigerian cocoa production

PurposeThe purpose of this study is to examine the relative importance of climate normals (average long-term temperature and precipitation) in explaining net farm revenue per hectare (NRh) for supplementary irrigated and rainfed cocoa farms in Nigeria.Design/methodology/approachNRh was estimated for 280 cocoa farmers sampled across seven Nigerian states. It was regressed on climate, household socio-economic characteristics and other control variables by using a Ricardian analytical framework. Marginal calculations were used to isolate the effects of climate change (CC) on cocoa farm revenues under supplementary irrigated and rainfed conditions. Future impacts of CC were simulated using Six CORDEX regional climate model (RCM) ensemble between 2036-2065 and 2071-2100.FindingsResults indicate high sensitivity of NRh to Nigerian climate normals depending on whether farms use supplementary irrigation. Average annual temperature increases and precipitation decreases are associated with NRh losses for rainfed farms and gains for supplementary irrigated cocoa farms. Projections of future CC impacts suggest a wide range of NRh outcomes on supplementary irrigated and rainfed farm revenues, demonstrating the importance of irrigation as an effective adaptation strategy in Nigeria.Originality/valueThis paper uses novel data sets for simulating future CC impacts on land values in Nigeria. CORDEX data constitute the most comprehensive RCMs projections available for Africa.

The hydraulic transfers “Setif-Hodna” to cope with impact of climate change on Setif high plains region

PurposeThe purpose of this paper is twofold: first, to show the impact of greenhouse gas emission scenarios on annual temperature and precipitation changes during three periods of the twenty-first century in Setif region by using two selected GCMs; and second, to show the importance of “Setif-Hodna” hydraulic transfers’ project, like a method to adapt to the water scarcity in the future.Design/methodology/approachThis study investigates likely changes in annual temperature and precipitation over Setif high plains region (North-East of Algeria) under four Special Report on Emission Scenarios scenarios: A1B, B1, A2 and B2, between three time slices: 2030, 2060 and 2090. MAGICC-SCENGEN 5.3v.2 was used as a tool for downscaling the two selected general circulation models.FindingsThe projections of GFDLCM20 and GFDLCM21 indicate that annual temperature will increase under the four scenarios and across the three time slices. GFDLCM20 predictions indicate a general decrease in mean annual precipitation across the four scenarios, with average of −3.02, −2.47 and −1.07 percent in 2030, 2060 and 2090, respectively. GFDLCM21 show a high decrease, with values of −18.72, −27.2 and −31.9 percent across the three periods, respectively.Originality/valueThis work is one of the first to study the impact of greenhouse gas emission scenarios on annual temperature and precipitation changes over the region, and present the hydraulic transfers project “Setif-Hodna” like an adaptive strategy to limit the effect of water scarcity in this region.

Drought and its effects on spring discharge regimes in Poland and Germany during the 2015 drought

ABSTRACTAreas of Western and Central Europe were severely affected by devastating droughts in 2003 and 2015. A sharp decrease in annual atmospheric precipitation led to diminished spring discharges. Analysis of the fluctuations in discharge from three groups of springs in the south of Poland, namely in the Sudetes and Carpathian mountains, and in the German province of Bavaria revealed an average discharge reduction ranging from 52 to 4%. The study proved the existence of a relationship between diminished groundwater recharge from precipitation and the type of rock forming the reservoir as well as the parameters of the rock in the drained catchment. Spring discharge regime was compared for various periods to show that a decline in the regime correlates with a decline in river flow rate; considering the continually changing weather patterns, this correlation is arguably a key factor in sustainable water management.

Climate change alters low flows in Europe under global warming of 1.5, 2, and 3 °C

Abstract. There is growing evidence that climate change will alter water availability in Europe. Here, we investigate how hydrological low flows are affected under different levels of future global warming (i.e. 1.5, 2, and 3 K with respect to the pre-industrial period) in rivers with a contributing area of more than 1000 km2. The analysis is based on a multi-model ensemble of 45 hydrological simulations based on three representative concentration pathways (RCP2.6, RCP6.0, RCP8.5), five Coupled Model Intercomparison Project Phase 5 (CMIP5) general circulation models (GCMs: GFDL-ESM2M, HadGEM2-ES, IPSL-CM5A-LR, MIROC-ESM-CHEM, NorESM1-M) and three state-of-the-art hydrological models (HMs: mHM, Noah-MP, and PCR-GLOBWB). High-resolution model results are available at a spatial resolution of 5 km across the pan-European domain at a daily temporal resolution. Low river flow is described as the percentile of daily streamflow that is exceeded 90 % of the time. It is determined separately for each GCM/HM combination and warming scenario. The results show that the low-flow change signal amplifies with increasing warming levels. Low flows decrease in the Mediterranean region, while they increase in the Alpine and Northern regions. In the Mediterranean, the level of warming amplifies the signal from −12 % under 1.5 K, compared to the baseline period 1971–2000, to −35 % under global warming of 3 K, largely due to the projected decreases in annual precipitation. In contrast, the signal is amplified from +22 (1.5 K) to +45 % (3 K) in the Alpine region due to changes in snow accumulation. The changes in low flows are significant for regions with relatively large change signals and under higher levels of warming. However, it is not possible to distinguish climate-induced differences in low flows between 1.5 and 2 K warming because of (1) the large inter-annual variability which prevents distinguishing statistical estimates of period-averaged changes for a given GCM/HM combination, and (2) the uncertainty in the multi-model ensemble expressed by the signal-to-noise ratio. The contribution by the GCMs to the uncertainty in the model results is generally higher than the one by the HMs. However, the uncertainty due to HMs cannot be neglected. In the Alpine, Northern, and Mediterranean regions, the uncertainty contribution by the HMs is partly higher than those by the GCMs due to different representations of processes such as snow, soil moisture and evapotranspiration. Based on the analysis results, it is recommended (1) to use multiple HMs in climate impact studies and (2) to embrace uncertainty information on the multi-model ensemble as well as its single members in the adaptation process.

Millennial multi-proxy reconstruction of oasis dynamics in Jordan, by the Dead Sea

Vegetation reconstructions in the Dead Sea region based on sediment records are potentially biased, because the vast majority of them derive from the western side of the sea, and only focus on large areas and time spans, while little is known about extra-local (< 1,000 m radius) to local (< 20 m radius) changes. To fill this gap, we compared a vegetation survey with modern pollen assemblages from the “Palm Terrace” oasis ca. 300 m b.s.l. (below sea level), at the eastern edge of the Dead Sea. This revealed how the oasis vegetation is reflected in pollen assemblages. In addition, two sediment cores were collected from the centre and the edge of a mire at the oasis to reconstruct past vegetation dynamics. We analysed sedimentary pollen and microscopic charcoal, as well as the sediment chemistry by X-ray fluorescence (XRF) and conductivity, focusing on the past ~ 1,000 years. Pollen results suggest that mesophilous Phoenix dactylifera (date palm) stands and wetland vegetation expanded there around ad 1300–1500 and 1700–1900. During the past ca. 100 years, drought-adapted Chenopodiaceae gained ground, partly replacing the palms. Results from elemental analysis, especially of elements such as chlorine, provide evidence of enhanced evaporative salinization. Increasing desertification and the associated decline of mesophilous date palm stands during the past ca. 50 years is probably related to a decrease in annual precipitation and also corresponds to decreasing water levels in the Dead Sea. These have mainly been caused by increasing extraction of fresh water from tributaries and wells, mainly for local agriculture and industry. In the future, with hotter and drier conditions as well as increased use of water, oasis vegetation along the Dead Sea might be at further risk of contraction or even extinction.

Impacts of Climate Change and Human Activities on the Three Gorges Reservoir Inflow

Identifying changes in runoff and quantifying the impacts of climate change and human activities are of great significance for water resources planning and management in a river basin. In this study, an inflow series of the Three Gorges Reservoir observed from 1951 to 2016 is used to identify the trend and abrupt change point by using statistical methods. Based on the meteorological data, soil type data, and land use data during the same period, the Soil and Water Assessment Tool (SWAT) model is established to quantitatively attribute changes in the Three Gorges Reservoir inflow to climate change and human activities separately and discuss the differences between the two-stage method, which divides the whole study period into two stages to analyze the reasons for runoff evolution, and multi-stage method, which divides the whole study period into more stages to consider the temporal and spatial variation of land use/cover (LULC). The results show: (1) During the study period, a significant decrease is detected in the Three Gorges Reservoir inflow and the decrease rate is 7.7 km3 per ten years, annual total precipitation decreases by −13.5 mm per ten years, and annual average temperature increases by 0.1 °C per ten years. (2) Contribution of climate change and human activities is around 7:3. Climate change is the main reason for the decrease in the Three Gorges Reservoir inflow. (3) Results of stages in multi-stage method are different from the result of two-stage method. Accumulative results of multi-stage method and result of two-stage method are consistent. There are some changes in results of every stage, which are different from the accumulative results.

Potential impacts of climate change on extreme precipitation over four African coastal cities

This study examines the impacts of climate change on characteristics of extreme precipitation events over four African coastal cities (Cape Town, Maputo, Lagos and Port Said) under two future climate scenarios (RCP4.5 and RCP8.5). Fourteen indices were used to characterise extreme precipitation and 16 multi-model simulation datasets from the Coordinated Regional Climate Downscaling Experiment (CORDEX) were analysed. The capability of the models to reproduce past characteristics of extreme precipitation over the cities was evaluated against four satellite datasets after quantifying the observation uncertainties over the cities. The models give realistic simulation of extreme precipitation characteristics over the cities, and in most cases, the magnitudes of the simulation biases are within the observation uncertainties. For both the RCP4.5 and RCP8.5 scenarios, the models project a decrease in wet days and an increase in dry spells over the four cities in the future. More intense daily precipitation is projected over Maputo, Lagos and Port Said. The intensity and frequency of extreme precipitation events are projected to increase over Lagos, but decrease over the other cities. A decrease in annual precipitation is projected over Cape Town, Maputo and Port Said, whilst an increase is projected over Lagos, where the water surplus from the more extreme precipitation events exceeds the deficit from the less wet days. A decrease in the number of widespread extreme events is indicated over all the cities. Wet-day percentile and all-day percentile methods signal opposite future changes in the extreme precipitation thresholds over the cities (except over Lagos). The results of this study may have application in managing the vulnerabilities of these coastal cities to extreme precipitation events under climate change.

Increasing drought effects on five European pines modulate Δ13C‐growth coupling along a Mediterranean altitudinal gradient

SummaryClimate warming increases vulnerability to drought in Mediterranean water‐limited forests. However, we still lack knowledge of the long‐term physiological responses of coexisting pine species in these forests regarding their ability to cope with warming‐induced drought stress.We investigated spatiotemporal patterns of tree performance for five isohydric pines with partially overlapping ecological niches in the eastern Iberian Peninsula along an altitudinal gradient:Pinus halepensis = Pinus pinaster ≤ Pinus nigra ≤ Pinus sylvestris ≤ Pinus uncinata.Using indexed tree‐ring widths (TRWi), we assessed the changes in the temporal coherence of radial growth (growth synchrony,âC) over the period 1902–2011 across three elevation belts: low ≈1100 m; mid = 1615 m; high = 2020 m. We also examined by mixed modelling whetherTRWishowed an increased coupling with leaf‐level gas exchange (inferred from indexed carbon isotope discrimination, Δ13Ci) by enhanced stomatal regulation in response to an amplified regional drought stress.Increasingly negative annual water balances (decrease in annual precipitation minus evapotranspiration = −4·8 mm year−1; 1970–2011) prompted more synchronous growth of coexisting pines between low‐ and mid‐elevation belts, withâCrising from 0·25 ± 0·04 (1902–1951) to 0·62 ± 0·05 (1962–2011). This effect was coupled with tighter stomatal regulation at mid‐elevation as indicated by high correlations betweenTRWiand Δ13Ci(&gt;0·60 from the mid‐1970s onwards) which resembled those found at low elevation. Simultaneously,TRWivs. Δ13Ciuncoupling occurred at the high‐elevation belt across species.Weaker growth‐climate relationships as elevation increased highlighted the major role of the altitude‐dependent thermal gradient in growth responsiveness to drought; however, an intensified Δ13Ciresponse to spring water availability across elevation belts observed from mid‐1970s onwards suggested regional shifts in tree physiological activity linked to earlier seasonal drought impacts. Warming‐induced drought stress is spreading to higher altitudes in Iberian pinewoods as multispecies growth is linked to progressively tighter stomatal control of water losses reflected in wood Δ13C.

Urban and peri-urban precipitation and air temperature trends in mega cities of the world using multiple trend analysis methods

Urbanization plays an important role in altering local to regional climate. In this study, the trends in precipitation and the air temperature were investigated for urban and peri-urban areas of 18 mega cities selected from six continents (representing a wide range of climatic patterns). Multiple statistical tests were used to examine long-term trends in annual and seasonal precipitation and air temperature for the selected cities. The urban and peri-urban areas were classified based on the percentage of land imperviousness. Through this study, it was evident that removal of the lag-k serial correlation caused a reduction of approximately 20 to 30% in significant trend observability for temperature and precipitation data. This observation suggests that appropriate trend analysis methodology for climate studies is necessary. Additionally, about 70% of the urban areas showed higher positive air temperature trends, compared with peri-urban areas. There were not clear trend signatures (i.e., mix of increase or decrease) when comparing urban vs peri-urban precipitation in each selected city. Overall, cities located in dry areas, for example, in Africa, southern parts of North America, and Eastern Asia, showed a decrease in annual and seasonal precipitation, while wetter conditions were favorable for cities located in wet regions such as, southeastern South America, eastern North America, and northern Europe. A positive relationship was observed between decadal trends of annual/seasonal air temperature and precipitation for all urban and peri-urban areas, with a higher rate being observed for urban areas.

System Dynamics Evaluation of Climate Change Adaptation Strategies for Water Resources Management in Central Iran

The Zayandeh-Rud River basin, Iran, is projected to face spatiotemporally heterogeneous temperature increase and precipitation reduction that will decrease water supply by mid-century. With projected increase (0.70–1.03 °C) in spring temperature and reduction (6–55%) in winter precipitation, the upper Zayandeh-Rud sub-basin, the main source of renewable water supply, will likely become warmer and drier. In the lower sub-basin, 1.1–1.5 °C increase in temperature and 11–31% decrease in annual precipitation are likely. A system dynamics model was used to analyze adaptation strategies taking into account feedbacks between water resources development and biophysical and socioeconomic sub-systems. Results suggest that infrastructural improvements, rigorous water demand management (e.g., replacing high water demand crops such as rice, corn, and alfalfa), and ecosystem-based regulatory prioritization, complemented by supply augmentation can temporarily alleviate water stress in a basin that is essentially governed by the Limits to Growth archetype.

Modeling the sedimentary response of a large Pyrenean basin to global change

Erosion processes at the catchment scale control a basin’s morphology and sediment patterns in the river network. Eroded sediments are transported and deposited downstream and may cause environmental problems and relevant effects on water storage and hydropower infrastructures. Quantification of water and sediment yield is complex due to the physical processes involved and their temporal and spatial variability, especially at the light of current global change. Numerical models that use spatially distributed information constitute a useful tool for these estimates, when sufficient input data are available. In this study, we applied the hydrological and sedimentological TETIS model to determine the patterns of water and sediment yield in a large mountain catchment. Flow discharge data obtained from two gauged stations were used for calibration and validation of the hydrological sub-model. Data from two reservoir bathymetries at the outlet of the study area were used for calibration of the sedimentological sub-model. After model calibration, several scenarios of climate and land use change were simulated. Climate scenarios show a general decrease in average annual precipitation and an increase in temperature, associated with an increase in extreme rainfall events. Global change scenarios lead to a counteracting effect between the increase in sediment transport during extreme events and the decrease in sediment erosion associated with afforestation following the abandonment of agricultural land. In the case of the most extreme climate scenario combined with total catchment deforestation, the model indicates a complete siltation of the reservoir by 2050. Model performance emphasizes its potential as a tool for evaluating water and sediment yield for large catchments, as well as of its usefulness for water and sediment management in light of future climate and land use change scenarios.

Future intensification of hydro-meteorological extremes: downscaling using the weather research and forecasting model

A set of ten downscaling simulations at high spatial resolution (3 km horizontally) were performed using the Weather Research and Forecasting (WRF) model to generate future climate projections of annual and seasonal temperature and precipitation changes over the Eastern Mediterranean (with a focus on Lebanon). The model was driven with the High Resolution Atmospheric Model (HiRAM), running over the whole globe at a resolution of 25 km, under the conditions of two Representative Concentration Pathways (RCP) (4.5 and 8.5). Each downscaling simulation spanned one year. Two past years (2003 and 2008), also forced by HiRAM without data assimilation, were simulated to evaluate the model’s ability to capture the cold and wet (2003) and hot and dry (2008) extremes. The downscaled data were in the range of recent observed climatic variability, and therefore corrected for the cold bias of HiRAM. Eight future years were then selected based on an anomaly score that relies on the mean annual temperature and accumulated precipitation to identify the worst year per decade from a water resources perspective. One hot and dry year per decade, from 2011 to 2050, and per scenario was simulated and compared to the historic 2008 reference. The results indicate that hot and dry future extreme years will be exacerbated and the study area might be exposed to a significant decrease in annual precipitation (rain and snow), reaching up to 30% relative to the current extreme conditions.