Increase In Extreme Precipitation Events Research Articles

Numerical simulation and validation of heavy rainfall flood inundation in small watersheds in undocumented mountainous areas

ABSTRACT With global warming and the increase in extreme precipitation events, floods are becoming more frequent in mountainous areas, and the safety of lives and property of people is seriously threatened. However, understanding of the flooding process in uninformative mountainous areas is limited due to the lack of high-quality hydrometeorological data. Hence, this study adopts the MIKE21 model to simulate flood inundation in the Shadai River basin in the Qilian Mountain region of the northern Tibetan Plateau as an example. This validates the model-simulated flow and inundation extent using the flow data obtained from the calculation of the flood trace points, extent of inundation, and high-resolution remote sensing images. The results show that the flash flood inundation mainly occurs at 12:00–01:00 AM on 18 August 2022, and the simulated and actual maximum inundation areas are 7.9 and 9.5 km2, respectively. The fitted F-statistic value is 0.81, and the relative error between the calculated flow rate of the flood trace point and the model-simulated flow rate is 8%, indicating good consistency. Furthermore, an in-depth exploration of the model parameter sensitivity reveals that the use of distributed Manning's roughness coefficient value has higher simulation accuracy.

Increasing monsoon precipitation extremes in relation to large-scale climatic patterns in Pakistan

This study comprehensively evaluates monsoon variability and its large-scale drivers in Pakistan, a country often affected by extreme monsoon events leading to destructive flooding. Utilizing the Monotonic Mann-Kendall and Sen's Slope test, we analyzed trends in seven indicators of extreme precipitation events (EPEs) from 1961 to 2017 across Pakistan and its homogeneous climatic regions. The wavelet coherence method further allowed us to probe the connection between EPEs and key climate indices such as the Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO), El Niño–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Pacific Decadal Oscillation (PDO), Indian summer monsoon (ISM), and Southern Oscillation Index (SOI) in the time-frequency domain. Our findings indicate a significant increase in all EPEs across Pakistan, particularly in the monsoon region (R-II) from 1961 to 2017, with a noticeable decline post-1980s. The findings revealed a significant increase in EPEs in the whole country from 1961 to 1989 to 1990–2017, with a dominant change in the monsoon region during 1990–2017. In terms of climate indices combinations, IOD + ISM showed the highest coherences (>0.65), while ENSO+IOD + ISM and ENSO+IOD + PDO displayed coherences >0.81 and > 0.79, respectively, across the entire country. The multi-linear regression (MLR) model analysis drivers indicate that IOD and ENSO are the leading drivers of changes in monsoon EPEs in the whole country, whereas the core monsoon region of Pakistan also showed a strong influence from AMO and NAO in tandem with ENSO and IOD. The overall increase in EPEs over Pakistan are mainly associated with the indices from the Pacific Ocean, especially IOD, ENSO and PDO and with their various combinations. Our study reveals the variations in EPEs across Pakistan, yielding insights that could inform water resource management strategies and disaster prevention measures.

Spatial patterns of short‐term extreme precipitation and their causes

AbstractThe spatial distribution of extreme precipitation significantly affects flow‐producing processes and flooding. Previous studies on heavy rainfall have mainly emphasized the temporal distribution characteristics, with little emphasis on rainfall spatial patterns. We objectively classified 3‐h scale extreme precipitation spatial patterns (EPSPs) in Guangdong Province, China. We calculated the importance of the influencing factors on EPSPs, analysed weather backgrounds corresponding to various EPSPs, and explained the causes of extreme precipitation. We found that the incidence of most EPSPs increased significantly over this 40‐year period, and this increase has been particularly pronounced since the beginning of the 21st century. The Pacific Decadal Oscillation (PDO) was found to be the main factor influencing the extreme precipitation events (EPEs) in western Guangdong, and the weakening of the PDO contributed to the occurrence of EPEs in these areas. Urbanization was the main factor contributing to the increase in EPEs in the southern and coastal areas of Guangdong. The EPSPs in central Guangdong were caused by a southwest jet stream and topographic uplift. Extreme precipitation in southern and coastal Guangdong was mainly triggered by the convergent shear of southwesterly winds. The EPSPs over western Guangdong were caused by the low vortex in western Guangdong and the influx of large amounts of water vapour from the southern ocean. This study has provided new ideas for the study of the formation process and mechanism of localized heavy precipitation as well as an important reference for the simulation of runoff in coastal areas.

Assess the impact of Climate Variability on potato yield using remote sensing data in Northern Finland

Understanding the impact of Climate Variability (CV) on crop yield is crucial for developing sustainable agriculture practices, especially in regions vulnerable to climate change. This study aims to identify the causes of the observed decline in potato yield in Northern Finland by analyzing Remote Sensing data and statistical analysis on climatic variables from 2001 to 2020. First, the exception years with critical production (2004, 2006, 2008, 2012, 2015) were selected based on the anomaly in the annual potato yield. Then a variety of extreme indices based on precipitation and Land Surface Temperature occurrence and intensity during the growing season were calculated to find how much impact they have on potato yield. Principal Component Analysis was used to select the most significant ones among the extreme indices. Finally, through a multiple regression analysis, we found that extreme precipitation events and cumulative temperature explain around 48 % potato yield variations in which extreme precipitation (with 38 %) had much more impact than cumulative temperature (with 10 %). We concluded that one degree increase in cumulative temperature increases potato yield by 19.64 kg/ha and in contrast, heavy precipitation plays a negative role, i.e., one day increase in extreme precipitation events, decreases potato yield by 2085 kg/ha.

Evolution of the Pingluo Section of the Upper Yellow River over the Past 50 Years: Responses to Environmental Change and Human Activity

The instability of the river channels has increased in response to the combined effects of global warming and human activity. This instability threatens the lives and property of people who live along river courses. This study takes the Pingluo section of the upper Yellow River, which is ~28 km long and ~400 m wide, as its research focus. We studied 11 periods of Landsat remote sensing images from 1973 to 2023 and analyzed the evolutionary characteristics of the Pingluo section over the past 50 years. The channel morphology indices included the channel braiding index (BIT), the bar braiding index (BIB), the average area of the bar (Ab), and the width of the wet channel area (BW). The results showed that there was an overall shrinking trend in this section of the Yellow River; more particularly, fluctuations in indicators such as the river width and the braiding index highlighted an increasing–decreasing–increasing pattern of change. During the 1973–1986 period, the river showed a widening trend, with narrow anabranches cutting through the floodplain and both the river width and the braiding index increasing dramatically over a short period. Over the 1986–2018 period, the area of the wet channel continued to shrink to its lowest level for the past 50 years, the river’s branches were diverted and abandoned, and the channel tended to straighten out. Between 2018 and 2023, the river showed a slightly expanding trend. The evolution of the river channel appears to be related to regional human activity and climate change. For example, after the joint filling of the Longyangxia and Liujiaxia reservoirs in the upper reaches of the Pingluo section of the Yellow River in 1986, runoff and sediment load along this section decreased, flood events became less frequent, and the channel tended to contract. In addition, the increase in extreme precipitation events over the last five years has led to an increase in the magnitude and frequency of peak discharge values in the region, which is the main reason for the increase in the river braiding index and area.

Multi-century (635-year) spring season precipitation reconstruction from northern Pakistan revealed increasing extremes

The Hindu Kush Himalaya region is experiencing rapid climate change with adverse impacts in multiple sectors. To put recent climatic changes into a long-term context, here we reconstructed the region’s climate history using tree-ring width chronologies of climate-sensitive Cedrus deodara and Pinus gerardiana. Growth-climate analysis reveals that the species tree-growth is primarily limited by moisture stress during or preceding the growing season, as indicated by a positive relationship between the chronology and precipitation and scPDSI, and a negative one with temperature. We have reconstructed 635 years (1384–2018 CE) of February–June precipitation using a robust climate reconstruction model that explains about 53% variance of the measured precipitation data. Our reconstruction shows several dry and wet episodes over the reconstruction period along with an increase in extreme precipitation events during recent centuries or years. Long, very wet periods were observed during the following years: 1392–1393, 1430–1433, 1456–1461, 1523–1526, 1685–1690, 1715–1719, 1744–1748, 1763–1767, 1803–1806, 1843–1846, 1850–1855, 1874–1876, 1885–1887, 1907–1909, 1921–1925, 1939–1944, and 1990–1992, while long dry periods were observed during the following years: 1398–1399, 1464–1472, 1480–1484, 1645–1649, 1724–1727, 1782–1786, 1810–1814, 1831–1835, 1879–1881, 1912–1918, 1981–1986, 1998–2003, and 2016–2018 CE. We found predominantly short-term periodicity cycles of 2.0, 2.2, 2.3, 2.4, 2.6–2.7, 2.9, 3.3, 4.8, 8.1–8.3, and 9.4–9.6 years in our reconstruction. Spatial correlation analyses reveal that our reconstruction is an effective representation of the precipitation variability in the westerly climate-dominated areas of Pakistan and adjacent regions. In addition to the influence of regional circulation systems like western disturbances, we found possible teleconnections between the precipitation variability in northern Pakistan and broader-scale climate modes or phases like AMO and ENSO. The study also highlights the prospects of tree-ring application to explore linkages between western disturbance, increasing intensity and frequency of extreme climate events, and analysis of long-term atmospheric circulation over the western Himalayan region.

Spatiotemporal variability in extreme precipitation and associated large-scale climate mechanisms in Central Asia from 1950 to 2019

Increased sea surface temperature, evaporation, air temperature, and moisture holding capacity associated with climate change may the enhance transport of moisture to Central Asia (CA), resulting in increased extreme precipitation events (EPEs). Changes in EPEs may affect the socioeconomic and ecological environment in typical arid and semi-arid regions of CA. Therefore, based on meteorological station data and four reanalyzed precipitation datasets, we used the Taylor diagram, Geo-Detector method, and other methods to examine 10 EPE indices in CA from 1950 to 2019, analyzed their spatial-temporal trends, and quantified the influence of large-scale climate factors on EPEs. The results showed that GSWP3_W5E5 was the optimal option with better performance in terms of monthly and annual precipitation in CA. Overall, EPEs in CA showed an increasing trend, but an abrupt point was found in 1986, when very wet day precipitation (R95p) increased from 36.64 to 47.84 mm; the increasing rate also changed from 0.8 to 5.06 mm/10a. The changes in the Northern Hemisphere Subtropical High Intensity Index (NSI), NINO B Area Sea Surface Temperature Anomaly Index (NINOB), Asian Zonal Circulation Index, and Atlantic Multidecadal Oscillation Index are the main reasons for the increase in EPEs; the NSI and NINOB had the largest contributions to EPEs, with at 44.32 % and 43.80 %, respectively. Additionally, two-factor interactions had a more significant influence. Further analysis revealed that the abnormal warming of sea surface temperature and others led to the strengthen of water vapor transport in CA caused by a series of cyclones and anticyclonic anomalies in the westerly circulation zone, leading to the increase of EPEs. The results obtained in this study can contribute to a more comprehensive understanding of the changes in EPEs and provide a reference for water resource management and disaster prevention in CA.

Change in extreme precipitation events: Exposure and vulnerability in the Poyang Lake Basin, China

On the basis of daily observations data from 1984 to 2020, the spatiotemporal characteristics of extreme precipitation events in the Poyang Lake Basin (China) were analyzed using the intensity–area–duration method. With consideration of spatially distributed data on gross domestic product (GDP), population, and disaster losses related to historical extreme precipitation events, the exposure and vulnerability of the population and GDP of the study area to extreme precipitation events were systematically assessed. The results revealed the following. 1) The intensity and frequency of extreme precipitation, as well as the area affected, showed trends of increase, especially in the northeast of the basin. 2) Population exposure in the basin showed a trend of increase of 2.43 million/a. Change in population exposure was greatest in the most recent 10 years, with an average increase of 6.64 million/a. Change in extreme precipitation was the primary driver of the rapid increase in population exposure. 3) The average annual GDP exposure of the basin was ¥5.43 billion, and economic exposure has increased substantially at an average rate of ¥0.56 billion/a. Unlike population exposure, the increase in economic exposure was driven mainly by rapid economic growth. 4) By constructing vulnerability curves of economic losses in different decades, the trend of economic vulnerability was found to have clearly declined, i.e., economic vulnerability in 2010 was 13.3 (4.1) times lower than that in the 1990s (2000s). Effective disaster prevention and reduction measures should urgently be adopted in the study area to mitigate the effects of increase in extreme precipitation events.

Functional diversity and soil nutrients regulate the interannual variability in gross primary productivity

Abstract Global change, encompassing rising temperatures and an increase in extreme precipitation events, has influenced vegetation photosynthesis; this can be seen in the gross primary productivity (GPP) of terrestrial ecosystems, which, over time affects the global carbon cycle. The impact of climate on interannual variability in GPP (GPPIAV) has been extensively explored in the literature. Other changing factors driven by global change, such as biodiversity and soil nutrient availability, are vital in predicting the future of the biosphere. However, the roles of these factors remain unclear. We combined (i) data from 454 community plots collected using standard protocols from 2013 to 2019 across China, (ii) plant trait data and phylogenetic information of more than 2500 plant species, and (iii) soil nutrient data that we measured. Using these data from 72 “real‐world” ecosystems located across a range of environmental conditions and species pools, we investigated the role of environmental factors including temperature, precipitation and soil nutrients and multifaceted diversity (i.e. species richness, hypervolume‐based functional diversity, and phylogenetic diversity) in mediating the magnitude of GPPIAV using multi‐model averaging and structural equation modelling. We found that soil nutrients and functional diversity are the main determinants of the magnitude of GPPIAV and that climate effects are predominantly mediated by multifaceted diversity. Synthesis. We provide strong evidence that ecosystems with higher biodiversity have less variable annual biomass production and decrease the extent of GPPIAV through compensatory effects across diverse ecosystems. Nutrient‐rich ecosystems are likely to buffer the impact of climate variability on ecosystem carbon uptake better than nutrient‐poor ecosystems. Our results demonstrate that biodiversity plays a crucial role in buffering the effects of environmental variability on carbon uptake in terrestrial ecosystems.

Projected changes in precipitation characteristics over the Drakensberg Mountain Range

AbstractThis study examines the potential impacts of climate change on the characteristics of precipitation over the Drakensberg Mountain Range (DMR) at different global warming levels (GWLs: 1.5, 2.0, 2.5 and 3.0°C) under the Representative Concentration Pathway 8.5 (RCP8.5) scenario, using dynamical and statistical downscaled datasets. The dynamical datasets consist of 19 multi‐model simulations datasets from the Coordinated Regional Climate Downscaling Experiment (CORDEX), whereas the statistical downscaled datasets comprise 19 multi‐model simulations from the National Aeronautics and Space Administration (NASA) Earth Exchange (NEX) Global Daily Downscaled Projections (NEX‐GDDP, hereafter NEX). The capacity of the CORDEX and NEX datasets to represent past characteristics of extreme precipitation over the DMR was evaluated against eight observation datasets. The precipitation characteristics were represented by eight precipitation indices. Both CORDEX and NEX realistically capture the characteristics of extreme precipitation over the Drakensberg and, in most cases, their biases lie within the observation uncertainty. However, NEX performs better than CORDEX in reproducing most of the precipitation characteristics, except in simulating the threshold of extreme rainfall. The ensemble means of CORDEX and NEX agree on a future increase in the intensity of normal precipitation, in the frequency and intensity of extreme precipitation, as well as an increase in widespread extreme events, with a decrease in the number of precipitation days and continuous wet days. However, they disagree on the projected changes of annual precipitation, for which CORDEX projects an increase over most parts of the DMR, whereas NEX indicates a decrease. The self‐organizing‐map analysis, which reveals diversity in the projection patterns hidden in the ensemble means, shows the most probable combinations of projected changes in the annual precipitation and extreme precipitation events (in terms of intensity and frequency): (a) increase in both annual precipitation and extreme precipitation events; (b) decrease in both annual precipitation and extreme precipitation events; (c) decrease in annual precipitation but increase in extreme precipitation events. The results of this study can thus provide a basis for developing climate change adaptation and mitigating strategies over the DMR.

Spatiotemporal dependence of soil moisture and precipitation over India

Anthropogenic climate change has impacted almost all phases of the global water cycle. Growing consensus asserts that extreme precipitation events will only rise in the years to come. However, an increase in extreme precipitation events does not necessarily correspond to higher flood risk. Much onus lies on the antecedent conditions before the storm events. Despite the importance of Soil Moisture (SM) – Precipitation (P) dependence in runoff generation, relatively few studies have unraveled the SM – P dependence. Previous studies were constrained by the direct trivial relationship existing between SM and P, and hence there is a need to understand direction and dynamical interdependency. We employed Event Coincidence Analysis (ECA) to identify and quantify the preconditioning of P extremes by soil moisture (SM) anomalies. High precursor coincidence rate (greater than45%) was obtained for traditional flash flood-prone areas over India - Ganga river basin, West-flowing rivers of Kutch and Saurashtra including Luni, inland drainage of Rajasthan and Narmada river basin, indicating the robustness of the approach. The trigger coincidence rate reveals strong SM-P coupling over central India. Our results indicate the applicability of ECA in characterizing the spatiotemporal patterns of SM-P dependence over India.

Hydrological Intensification Will Increase the Complexity of Water Resource Management

AbstractGlobal warming intensifies the hydrological cycle by altering the rate of water fluxes to and from the terrestrial surface, resulting in an increase in extreme precipitation events and longer dry spells. Prior hydrological intensification work has largely focused on precipitation without joint consideration of evaporative demand changes and how plants respond to these changes. Informed by state‐of‐the‐art climate models, we examine projected changes in hydrological intensification and its role in complicating water resources management using a framework that accounts for precipitation surplus and evaporative demand. Using a metric that combines the difference between daily precipitation and daily evaporative demand (surplus events) and consecutive days when evaporative demand exceeds precipitation (deficit time), we show that, globally, surplus events will become larger (+11.5% and +18.5% for moderate and high emission scenarios, respectively) and the duration between them longer (+5.1%; +9.6%) by the end of the century, with the largest changes in the northern latitudes. The intra‐annual occurrence of these extremes will stress existing water management infrastructure in major river basins, where over one third of years during 2070–2100 under a moderate emissions scenario will be hydrologically intense (large intra‐annual increases in surplus intensity and deficit time), tripling that of the historical baseline. Larger increases in hydrologically intense years are found in basins with large reservoir capacity (e.g., Amazon, Congo, and Danube River Basins), which have significant populations, irrigate considerable farmland, and support threatened and endangered aquatic species. Incorporating flexibility into water resource infrastructure and management will be paramount with continued hydrological intensification.

Future precipitation in a Mediterranean island and streamflow changes for a small basin using EURO-CORDEX regional climate simulations and the SWAT model

Climate change effect analysis on the hydrologic cycle is essential for the assessment of water management strategies. Climate models can provide projections of precipitation changes in the future, based on greenhouse gas emissions scenarios. In this study the EURO-CORDEX (European COordinated Regional Downscaling Experiment) climate models were first analyzed for the island of Sardinia, against observed precipitation for the historical period of 1976–2005. A Multi-Model Ensemble (ENS) was built, weighting different models based on their performance against observed precipitations. Future projections (2071–2100) were analyzed using the 8.5 RCP emissions scenario to evaluate changes in precipitations. Climate models were then used as climate forcing for the SWAT model (Soil and Water Assessment Tool), aiming to evaluate the effects of such changes on streamflow and runoff of two small catchments located in the South-West Sardinia. A general decrease of mean precipitation values, up to 25 % at yearly scale in South-West Sardinia, is expected for the future, along with an increase of extreme precipitation events. Especially in the eastern and southern areas, extreme events are projected to increase by 30%. Such changes reflect on the hydrologic cycle with a decrease of mean streamflow (ranging from −18% to −25%) and runoff (ranging from −12% to −18%), except in spring, when runoff is projected to increase by 20–30%. This study contributes to the analysis of climate change impacts in the Mediterranean, which is considered a hotspot of the global warming, enhancing the use of modeling tools to investigate possible future scenarios.

Analysing the Impact of Climate Change on Hydrological Ecosystem Services in Laguna del Sauce (Uruguay) Using the SWAT Model and Remote Sensing Data

Assessing how climate change will affect hydrological ecosystem services (HES) provision is necessary for long-term planning and requires local comprehensive climate information. In this study, we used SWAT to evaluate the impacts on four HES, natural hazard protection, erosion control regulation and water supply and flow regulation for the Laguna del Sauce catchment in Uruguay. We used downscaled CMIP-5 global climate models for Representative Concentration Pathways (RCP) 2.6, 4.5 and 8.5 projections. We calibrated and validated our SWAT model for the periods 2005–2009 and 2010–2013 based on remote sensed ET data. Monthly NSE and R2 values for calibration and validation were 0.74, 0.64 and 0.79, 0.84, respectively. Our results suggest that climate change will likely negatively affect the water resources of the Laguna del Sauce catchment, especially in the RCP 8.5 scenario. In all RCP scenarios, the catchment is likely to experience a wetting trend, higher temperatures, seasonality shifts and an increase in extreme precipitation events, particularly in frequency and magnitude. This will likely affect water quality provision through runoff and sediment yield inputs, reducing the erosion control HES and likely aggravating eutrophication. Although the amount of water will increase, changes to the hydrological cycle might jeopardize the stability of freshwater supplies and HES on which many people in the south-eastern region of Uruguay depend. Despite streamflow monitoring capacities need to be enhanced to reduce the uncertainty of model results, our findings provide valuable insights for water resources planning in the study area. Hence, water management and monitoring capacities need to be enhanced to reduce the potential negative climate change impacts on HES. The methodological approach presented here, based on satellite ET data can be replicated and adapted to any other place in the world since we employed open-access software and remote sensing data for all the phases of hydrological modelling and HES provision assessment.

Risk Reduction Framework for Blue-Green Roofs

As climate change in the Nordic region brings an increase in extreme precipitation events, blue-green roofs have emerged as a solution for stormwater management, hereafter referred to as “blue-green roofs”. The addition of blue-green layers on a conventional compact roof represents several multi-disciplinary technical challenges and quality risks that must be managed. This paper aims to list and address the key building technical challenges associated with blue-green roofs and to present a framework for managing these risks. Literature and document studies as well as qualitative interviews and expert meetings have been conducted to collect research data on defects in blue-green roofs and causes thereof. A list of nine key challenges has been extracted along with recommendations on how to address them. The recommendations are structured around a framework developed for practical use in building projects. For ease of use, the nine key challenges are presented on a general level, with references to detailed recommendations. The framework is intended to be used to reduce the building technical risks of blue-green roofs, by addressing the most important quality risk elements.

Changes in Slight and Extreme Precipitation Events From 1963 to 2017 Over Northern Xinjiang, China

Based on daily measured data from 25 stations in Xinjiang Province from 1963 to 2017, we discuss the statistical characteristics, linear trends, and temporal concentration of slight precipitation (SP) and extreme precipitation (EP) events, and consider relationships between SP and EP events and daily mean temperature. The results show that SP events contribute strongly to the total annual number of wet days, and that EP events contribute strongly to the total annual precipitation amount. In consist with the decrease in SP events and the increase in EP events over the 55-year period, the contribution of SP events to total annual number of wet days has decreased significantly while the contribution of EP events to total annual precipitation amount has increased significantly. SP event usually distributes through most months of the year, whereas EP event usually concentrates in summer (JJA). Influenced by the negative trends for SP events frequency and positive trends of EP events frequency during recent decades, the concentration degree for SP and EP events have significantly increased and decreased, respectively. Distinct differences are found between the relationships of SP events and EP events to daily mean temperature. The daily mean temperature recorded at the stations in Northern Xinjiang on days with SP events was between –35°C and +34°C, and for EP events ranged from –21°C to +30°C. Regionally averaged curves for the change in SP and EP event frequency with temperature have bimodal and unimodal distributions, respectively. Trends for daily mean temperatures and for the frequency of SP events at different temperatures agree well over nearly the entire temperature range, while trends for daily mean temperatures and for the frequency of EP events at different temperatures are not always consistent. These results will help to improve our understanding of the characteristics and variability of precipitation in arid regions within the context of climate warming.

Projections of river floods in Europe using EURO‐CORDEX, CMIP5 and CMIP6 simulations

AbstractA large ensemble of hydroclimatic simulations is used to simulate the occurrence of river floods over Europe in a climate change context. A river routing model derived from a distributed hydrological model (CHyM) is forced with 44 EURO‐CORDEX, 13 CMIP5 and 7 CMIP6 simulations to assess the effects of climate change on the flood magnitude under two different scenarios. The impact of climate change is evaluated using a 100‐year return period discharge indicator (Q100). Results show a decrease in magnitude of Q100 flood events over the Mediterranean, Scandinavia and north eastern Europe. This latter signal appears particularly robust and in contrast to the projected mean flow signal, which is shown to increase by the end of the century in response to increased mean precipitation. The reduction of snow accumulation during winter induced by a large increase of late winter temperatures is the main reason behind the decrease of floods over the North Eastern regions. An opposite signal is projected over Great Britain, Ireland, Northern Italy and Western Europe, where a robust signal of flood magnitude increase is evident, being driven by an increase of extreme precipitation events. All these simulations are intended for use in impact assessment studies towards the development of suitable response options.

Change detection based flood mapping using multi-temporal Earth Observation satellite images: 2018 flood event of Kerala, India

ABSTRACT The future projections of climate change envisage a global increase in extreme precipitation events and subsequent flooding. The reliable and rapid flood maps are the critical parameters in preparing the disaster management plans. This study demonstrated an effective flood mapping framework using freely available multi-temporal Earth Observation (EO) images, including C-band Sentinel-1A & 1B Synthetic Aperture Radar (SAR) images and optical WorldView-3 images, for analyzing the 2018 flood event of Kerala, India. Two Change Detection (CD) techniques, i.e. Ratio Index (RI) and Normalized Change Index (NCI) combined with semi-automatic thresholding are implemented on temporal descending pass SAR images for flood identification. For ascending pass SAR images, the statistical-based thresholding method is implemented. The results indicate that combined use of ascending and descending pass SAR images contributed to a better understanding of flood conditions. It is also inferred that the use of a pre-flood image can enhance flood area estimation and helps in minimizing the overestimation errors. The results also found that NCI outperforms RI for Kerala flood event. Flood area extracted from these techniques is plotted against the Indian Meteorological Department (IMD) rainfall datasets, which showed a similar trend. Field photographs and optical images are used for validation purposes.

Dissolved organic matter protects mosquito larvae from damaging solar UV radiation.

Mosquitoes have increased in their abundance and geographic distribution in northeastern North America, coinciding with an increase in extreme precipitation events and up to a doubling of dissolved organic matter (DOM) concentrations in some inland waters. Increases in DOM can reduce exposure of mosquito larvae to solar ultraviolet (UV) radiation. Although mosquito larvae are most common in shaded habitats, almost nothing is known about their susceptibility to damage by solar UV radiation, or the ability of DOM to create a refuge from damaging UV in their shallow-water habitats. We hypothesize that 1) exposure to solar UV radiation is lethal to mosquito larvae, 2) larvae lack photo-enzymatic repair to fix UV-damaged DNA, and 3) DOM shades larvae from lethal solar UV radiation. We tested these hypotheses with experiments that manipulated UV radiation, the photo-repair radiation necessary for photo-enzymatic DNA repair, and DOM. Exposure to solar UV radiation significantly decreased larval survivorship, while DOM significantly increased it. There was no evidence of photo-enzymatic DNA repair. Our findings confirm that solar UV radiation decreases habitat suitability for mosquito larvae, but DOM provides a refuge from UV. This highlights the need for vector control managers to prioritize high DOM and shaded habitats in their efforts to reduce mosquito populations.

New perspectives on ‘warming–wetting’ trend in Xinjiang, China

Recently, a hot topic about warmer and wetter climate change in the arid region of Northwest China, especially in Xinjiang, has attracted much attention by general public and scientific community. This study revisits this topic especially for Xinjiang in the Eurasian continental context from multiple perspectives based on most updated CRU high-resolution grid data and China's homogenized station data in 1961–2019. We conclude that such ‘warming–wetting’ trend is not a regional phenomenon for Xinjiang but has much larger spatial scale. Regions having experienced both temperature and precipitation increases reflecting ‘warming–wetting’ trend account for more than half of the Eurasian continent since 1961. Nevertheless, the ‘warming–wetting’ trend in Xinjiang suggests some unique regional features in response to the global warming. Although drought seems to have relieved to some extent, especially in the mountainous regions in western Xinjiang, the nature of arid and semi-arid climate regime has not changed. Noticeably, the interannual variability of precipitation has enlarged and the increase in extreme precipitation events has a major contribution. These findings suggest that ‘warming–wetting’ trend in Xinjiang is asymmetric regarding warming and wetting in seasons and intensifying interannual variability and increasing contribution of extreme precipitation to the total. Thus, the current ‘warming–wetting’ trend in Xinjiang possibly brings us some beneficial impacts for the ecosystem but also increases challenges for water resources utilization and risk management.