A synthetic view of rainfall intensification in the West African Sahel

The West African Sahel has been facing for more than 30 years an increase in extreme rainfalls with strong socio-economic impacts. This situation challenges decision-makers to define adaptation strategies in a rapidly changing climate. The present study proposes (i) a quantitative characterization of the trends in extreme rainfalls at the regional scale, (ii) the translation of the trends into metrics that can be used by hydrological risk managers, (iii) elements for understanding the link between the climatology of extreme and mean rainfall. Based on a regional non-stationary statistical model applied to in-situ daily rainfall data over the period 1983-2015, we show that the region-wide increasing trend in extreme rainfalls is highly significant. The change in extreme value distribution reflects an increase in both the mean and variability, producing a 5%/decade increase in extreme rainfall intensity whatever the return period. The statistical framework provides operational elements for revising the design methods of hydraulic structures which most often assume a stationary climate. Finally, the study shows that the increase in extreme rainfall is more attributable to an increase in the intensity of storms (80%) than to their occurrence (20%), reflecting a major disruption from the decadal variability of the rainfall regime documented in the region since 1950.

Sensoriamento Remoto Aplicado na Geoespacialização do Reservatório Poço da Cruz - PE e seu Entorno

O Sertão Pernambucano é caracterizado por longos períodos de secas, com um regime pluviométrico inconstante e irregular, dificultando o desenvolvimento socioeconômico da região. Neste contexto a aplicação de técnica de Sensoriamento Remoto utilizando de imagens georreferenciadas destaca-se pela relevância no monitoramento e análise da variação da cobertura vegetal e do suprimento hídrico nos reservatórios da região. Este estudo objetivou-se em avaliar as variações temporais geoespacializadas do uso e ocupação do solo, vegetação e área superficial do espelho d’água do reservatório de Poço da Cruz - PE, em uma perspectiva espectro temporal utilizando imagens datadas de 2000, 2013 e 2020, aplicando os índices espectrais MNDWI, NDWI, SAVI, IAF, dos sistemas sensores TM Landsat 5 e OLI Landsat 8, e ferramentas do projeto MAPBIOMAS da coleção 5.0. A análise do MNDWI identificou o aumento na área superficial do reservatório ao longo dos anos, ressaltando que os anos de 2000 e 2013 apresentaram um maior estresse hídrico com redução dos valores do índice. Os índices NDWI, SAVI e IAF, apontaram uma cobertura vegetal escassa e seca com baixa umidade para os anos de 2000 e 2013, entretanto, observou-se o aumento do vigor vegetativo e presença de maior umidade para o ano de 2020. Condizente com os dados obtidos para o uso e ocupação do solo pelo projeto MAPBIOMAS, indicando que houve um aumento das áreas destinadas a agricultura e pastagem no entorno do reservatório entre os anos de 2000 e 2013, bem como o incremento do seu espelho d´água. Analysis of the Temporal Variability of Water Body in the Backwoods of the Pernambuco A B S T R A C TThe Sertão Pernambucano is characterized by long periods of drought, with an unstable and irregular rainfall regime, which hinders the socioeconomic development of the region. In this context, the application of the Remote Sensing technique using georeferenced images stands out for its relevance in monitoring and analyzing the variation in vegetation cover and water supply in the region's reservoirs. This study aimed to evaluate the geospatial temporal variations of the use and occupation of the soil, vegetation and surface area of the water mirror of the Poço da Cruz reservoir - PE, in a temporal spectrum perspective using images dated from 2000, 2013 and 2020, applying the spectral indices MNDWI, NDWI, SAVI, IAF, from the TM Landsat 5 and OLI Landsat 8 sensor systems, and tools from the MapBiomas project from the 5.0 collection. The MNDWI analysis identified the increase in the surface area of the reservoir over the years, noting that the years 2000 and 2013 showed greater water stress with a reduction in the index values. The NDWI, SAVI and IAF indexes indicated a sparse and dry vegetation cover with low humidity for the years 2000 and 2013, however, there was an increase in vegetative vigor and the presence of higher humidity for the year 2020. data obtained for land use and occupation by the MapBiomas project, indicating that there was an increase in areas for agriculture and pasture around the reservoir between 2000 and 2013, as well as an increase in its water surface.Keywords: biophysical indices; water resource; remote sensing.

Variability of ecosystem carbon source from microbial respiration is controlled by rainfall dynamics

Soil heterotrophic respiration (Rh) represents an important component of the terrestrial carbon cycle that affects whether ecosystems function as carbon sources or sinks. Due to the complex interactions between biological and physical factors controlling microbial growth, Rh is uncertain and difficult to predict, limiting our ability to anticipate future climate trajectories. Here we analyze the global FLUXNET 2015 database aided by a probabilistic model of microbial growth to examine the ecosystem-scale dynamics of Rh and identify primary predictors of its variability. We find that the temporal variability in Rh is consistently distributed according to a Gamma distribution, with shape and scale parameters controlled only by rainfall characteristics and vegetation productivity. This distribution originates from the propagation of fast hydrologic fluctuations on the slower biological dynamics of microbial growth and is independent of biome, soil type, and microbial physiology. This finding allows us to readily provide accurate estimates of the mean Rh and its variance, as confirmed by a comparison with an independent global dataset. Our results suggest that future changes in rainfall regime and net primary productivity will significantly alter the dynamics of Rh and the global carbon budget. In regions that are becoming wetter, Rh may increase faster than net primary productivity, thereby reducing the carbon storage capacity of terrestrial ecosystems.

Evaluating landslide response in a seismic and rainfall regime: a case study from the SE Carpathians, Romania

There have been many studies exploring rainfall-induced slope failures in earthquake-affected terrain. However, studies evaluating the potential effects of both landslide-triggering factors – rainfall and earthquakes – have been infrequent despite rising global landslide mortality risk. The SE Carpathians, which have been subjected to many large historical earthquakes and changing climate thus resulting in frequent landslides, comprise one such region that has been little explored in this context. Therefore, a massive (∼9.1 Mm2) landslide, situated along the river Bâsca Rozilei, in the Vrancea seismic zone, SE Carpathians, is chosen as a case study area to achieve the aforesaid objective (evaluating the effects of both rainfall and earthquakes on landslides) using slope stability evaluation and runout simulation. The present state of the slope reveals a factor of safety in a range of 1.17–1.32 with a static condition displacement of 0.4–4 m that reaches up to 8–60 m under dynamic (earthquake) conditions. The groundwater (GW) effect further decreases the factor of safety and increases the displacement. Ground motion amplification enhances the possibility of slope surface deformation and displacements. The debris flow prediction, implying the excessive rainfall effect, reveals a flow having a 9.0–26.0 m height and 2.1–3.0 m s−1 velocity along the river channel. The predicted extent of potential debris flow is found to follow the trails possibly created by previous debris flow and/or slide events.

A Clustering Routing Algorithm for Wireless Sensor Monitoring Network in Irrigation Area

It is the basis for the implementation and scientific management decision of precision irrigation to accurately and comprehensively sense water and rainfall regime, soil moisture content and engineering conditions in irrigation areas and various environmental factors closely related to crop growth. In view of the characteristics of large monitoring range and scattered distribution of measuring points in the irrigation area, based on the analysis of the characteristics of the strip shape layout of the wireless sensor network at the water demand side of the irrigation area, and the limited battery energy and transmission distance under the condition of battery power supply, a clustering routing algorithm based on wireless sensor network for monitoring irrigation area is proposed (known simply as CRAIM algorithm). The formation of clusters, the selection of cluster heads, the routing process between clusters and the sink nodes are studied, and the CRAIM algorithm, EE-LEACH (energy-efficient LEACH) and MMH-LEACH (modified multi-hop LEACH) algorithm are simulated and compared respectively. Experimental results showed that, the new algorithm, CRAIM, has some advantages in the energy consumption of the network.

Regionalization of Rainfall Regimes Using Hybrid RF-Bs Couple with Multivariate Approaches

Monthly precipitation data during the period of 1970 to 2019 obtained from the Meteorological, Climatological and Geophysical Agency database were used to analyze regionalized precipitation regimes in Yogyakarta, Indonesia. There were missing values in 52.6% of the data, which were handled by a hybrid random forest approach and bootstrap method (RF-Bs). The present approach addresses large missing values and also reduces the Root Mean Square Error (RMSE) and the Mean Absolute Error (MAE) in the search for the optimum minimal value. Cluster analysis was used to classify stations or grid points into different rainfall regimes. Hierarchical clustering analysis (HCA) of rainfall data reveal the pattern of behavior of the rainfall regime in a specific region by identifying homogeneous clusters. According to the HCA, four distinct and homogenous regions were recognized. Then, the principal component analysis (PCA) technique was used to homogenize the rainfall series and optimally reduce the long-term rainfall records into a few variables. Moreover, PCA was applied to monthly rainfall data in order to validate the results of the HCA analysis. On the basis of the 75% of cumulative variation, 14 factors for the Dry season and the Rainy season, and 12 factors for the Inter-monsoon season, were extracted among the components using varimax rotation. Consideration of different groupings into these approaches opens up new advanced early warning systems in developing recommendations on how to differentiate climate change adaptation- and mitigation-related policies in order to minimize the largest economic damage and taking necessary precautions when multiple hazard events occur.

Identification of changes in the rainfall regime in Chihuahua's state (México)

The impacts of Climate Change are not homogeneous globally or for a country or region as a whole. Consequently, it is essential to carry out studies to identify its effects in particular areas. Due to its geographical and topographic characteristics, Chihuahua's state is vulnerable to the adverse effects of Climate Change. The scarce availability of water resources leads to problems of social pressure and economic impact. This paper analyzes the alteration of the rainfall regime in Chihuahua's state and its association with Climate Change. For this, historical characterization is used; trend analysis using the Mann Kendall test; and calculation of 10 indices of climatic extremes proposed by the Group of Experts for Detection and Climate Change Indices for the precipitation variable. The results showed that the precipitation patterns in the south and southeast of Chihuahua's state have been gradually modifying, with a downward trend in annual accumulated and reduction of wet days. Still, in counterpart, there is a slight intensification of extreme rainfall. This fact added to the growing demand for water resources in the entity, requests for public policies for sustainable management and responsible use by users. Otherwise, there is a risk of experiencing negative effects associated with the over-exploitation of water, not only for the resource users but also for the environment.

Morphology, sedimentology and origin of an anomalous cut-off along the Pravara river, deccan trap region, India

River meanders have always been an intriguing subject in fluvial geomorphology because of their ubiquity, dynamism, remarkable forms and practical consequences of their movement. Sometimes a relatively straight channel flowing over bedrock may develop a lone meander bend cut-off which is very out of the place from the surrounding area. The occurrence of a sudden bend along a river may not be a meandering bend but may be manifestation of sudden change in the river dynamism due to many reasons, such as, lithology, change in rainfall regime, tectonics etc. The formation of such features highlights the behavior of river in the past. One such striking feature has been observed along the River Pravara in the Deccan Trap Region, Maharashtra, India. Rivers in Deccan Trap Region do not meander and form cut-offs by rule. It is rocky country where rivers flow in deeply incised bedrock. Hence, the observed feature displays a striking anomaly in this region. Hence, an attempt has been made in the present paper to evaluate the mode of formation of this single cut-off along this channel. Morphological and sedimentological data were generated and analyzed for the channel loop and the link channel to understand the competence of the river in the past and present which were directly or indirectly responsible for the development of this channel anomaly in this reach. Based on the results of the analysis and intensive field observations, it has been inferred that this is a classic example of natural morphological adjustment of a river when a set of events occurred, first retardation of vertical erosion encountering bedrock followed by series of floods to induce the channel to divert from the original path to resume the present course. Presence of a tributary further aided to the process of the loop development. The study can provide additional knowledge to the studies involving anomalous channel cut-offs at any part of the world.

Partial exclusion of precipitation: throughfall, stemflow and canopy interception in Eucalyptus plantations in southern Brazil

Hydrological behavior in reforested watersheds is different from that under other forms of cover. The variation may be related to aspects intrinsic to species, planting density, physiological maturity, management system and climatic conditions. Periodically, climatic anomalies such as the case of La Ninã are observed, and these are responsible for the alteration of the rainfall regime and consequently generate water deficits in the southern region of Brazil. Water deficit is responsible for reducing growth and productivity for the Eucalyptus genus, in addition to causing changes in hydrological behavior in reforested watersheds. Accordingly, this study compared the partition of rainfall in throughfall, stemflow and canopy interception of eucalyptus trees submitted or not to partial exclusion of precipitation. In the open field, 3 rainfall collectors were installed, and in the stand, for each rain exclusion treatment, 9 throughfall collectors and 9 stemflow collectors were installed. Every two weeks for 12 months, the volume of the collectors was measured. The quantified precipitation was 1627 mm over a year. In the treatment without exclusion, 84.8, 2.9 and 12.3% referred to throughfall, stemflow and canopy interception, respectively, while in the treatment excluding rainfall 80.6, 2.3 and 17.2% referred to throughfall, stemflow and canopy interception. The regression adjustments for throughfall and stemflow showed satisfactory R2 coefficients.