Explore the vast range of titles available.

Since the 1990s, rainfall has been reported to increase over the Gulf of Guinea. In light of the devastating floods that have occurred since then over the coastal areas of this region, this study aims to better characterize the recent trends in precipitation there. We used the Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) product, a new observational rainfall dataset that covers the period 1981−2014 at high resolution and daily time steps. During the first rainy season (April−June), we find that the lack of significant trend observed in mean precipitation hides a trend towards less frequent but more intense rainfall along the coast of the Gulf of Guinea, which is expected to increase the likelihood of flooding and droughts, and fits with the recent increase in devastating floods. Over the north however (between 7° and 12.5° N), rainfall has become more frequent and less intense, which is expected to decrease the likelihood of flooding and droughts. During the second rainy season (September − November), we find that the clear increase in mean precipitation observed between 5° and 12.5°N results from an increase in precipitation intensity and frequency, while over southern Cameroon, the decrease in mean precipitation hides a trend towards less frequent but more intense rainfall. In both seasons, the average duration of wet spells has greatly decreased along the coast, in favor of more numerous and more intense isolated wet days.

Under the possible impact of climate warming, recent changes in dry and wet spells have contributed significantly to climate-related hazards around the world. In this work, spatial and temporal variations in dry and wet spells over Canada are investigated using daily precipitation data from 1979 to 2018. The time-varying relationships between precipitation spells and large-scale climate anomalies are modeled using a nonstationary generalized extreme value (GEV) distribution and Bayesian quantile regression. Over the period 1979–2018, significant changes in dry and wet spells have been observed across Canada, particularly in the southern Canadian Prairies (CP), where both the number and duration of dry spells show positive trends. Dry and wet spells over many parts of Canada are nonstationary under the effects of the El Niño–Southern Oscillation (ENSO) and the Pacific–North American pattern (PNA), with PNA having stronger effects on annual maximum dry spells than ENSO, especially in the central CP and eastern Ontario. For western Canada, the influence of ENSO on dry spells tends to be relatively strong, especially for dry spells of high quantiles, as El Niño generally induces atmospheric moisture deficit. For central Canada, ENSO and PNA have a negative (positive) impact on the wet spell duration of low (high) quantiles. For eastern Canada, PNA is negatively correlated with the duration of wet spells, especially for wet spells of high quantiles. Therefore, a better understanding of the spatial and temporal variability in dry and wet spell return periods will be useful for the effective management of water resources, and for developing effective disaster mitigation measures against the possible social and economic impacts of climate-related hazards.

The long-term fluctuations in dry-wet spells were assessed at standard meteorological week (SMW) over India using Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) rainfall data. The weekly sum of rainfall was embedded in Markov Chain Probability Model in Google Earth Engine (GEE) platform to compute initial and conditional probabilities of dry-wet spells during 2009-2020. An effective monsoon window (23rd SMW-39th SMW) was identified where initial probabilities (IPs) of dry (Pd) and wet (Pw) spells intersect at 50% probability level. Significant spatiotemporal variation of IPs was observed with initiation and withdrawal of monsoon over India. The analysis of co-efficient of variation (CV) showed low CV (<60%) in Pd and high CV (>60%) in Pw in semi-arid and arid regions whereas northern, central and eastern regions observed high CV (>60%) in Pd and low CV (<40%) in Pw. The drought prone and moisture sufficient zones were indentified based on the analysis of long-term frequency distribution of dry-wet spells and trend. Inter-comparison of IPs between CHIRPs with IMD (Indian Meteorological Department) and NOAA CPC (National Oceanic and Atmospheric Administration/Climate Prediction Centre) showed encouraging results. The study provides baseline reference for climate-resilient agricultural crop planning with respect to food security.

This study explores variations and trends in dry/wet days and spells over Banas River basin during 1961–2020. For this, daily rainfall data acquired from Water Resources Department of Rajasthan, India have been utilised. The variations have been identified in relation to number (dry/wet days and spells), mean and maximum length of dry/wet spells. For identifying trends, Mann–Kendall (MK), innovative trend analysis (ITA) and Sen’s slope estimator tests have been executed, whereas change points have been detected with the help of Pettit, Buishand range, standard normal homogeneity and Neumann ratio tests. In Banas River basin, dry days have been found much higher (330 days) as compared to wet (35 days), while the number of dry/wet spells has been found almost identical (18). A decreasing trend in dry days has been detected, whereas wet days have increased. In addition, change point detection tests have detected 1993 as the year of noteworthy change in dry/wet days and spells, whereas most of the stations witnessed such change in 1995 and 2009. These results will be valuable for water resource and risk reduction managers in managing the risks of drought and flood over the Banas River basin.

Climate services provide information on El Niño-Southern Oscillation (ENSO) evolution and predicted seasonal precipitation, broadly used by decision makers from the agriculture sector. However, soil moisture participates in a more complex soil–atmosphere interaction at subseasonal scale. This work aims to identify the ENSO signal on subseasonal precipitation indices and to assess soil moisture response during austral spring–summer over the southern Argentine Pampas. From daily precipitation, 16 indices were analyzed, and the temperature vegetation dryness index (TVDI) was computed as representative of soil moisture availability. In general, the different precipitation indices presented coherence with wetter (drier) climate conditions under the El Niño (La Niña) phase. A strong signal was found for precipitation frequency in November and accumulation in December, whereas reversal and a weak signal was observed during January, crucial for summer crops. The analysis of soil–moisture interaction suggests that positive precipitation anomalies during El Niño can be reinforced by high soil moisture stored in previous months (e.g., during El Niño 2002–2003). The drying process increases in soils with low water retention capacity, producing a spatially heterogeneous impact (e.g., El Niño 2009–2010). The dry pattern expected for La Niña events was observed in 2007–2008, affecting regions with high water retention and productivity. In addition, long wet spells presented a stronger influence in these regions. Owing to the spatial and temporal heterogeneity observed at subseasonal scale, this study suggests the need for the joint analysis of atmospheric variables and soil moisture content for medium-term agricultural planning in the context of ENSO events in the southern Argentine Pampas.

Half-hourly ground-based GPS measurements of precipitable water vapor (PWV) from January 2009 to December 2012 are analyzed to investigate their potential for hydrological applications at basin level. In particular, the usefulness of these high temporal resolution data for monitoring extreme weather conditions, such as floods and meteorological dry/wet spells, is discussed. Two sample GPS stations in U.S. from the SoumiNet network are considered that have rather continuous data for the last four years and a few missing values. Results suggest that: (i) A flood event is characterized by an anomalous increase of PWV accompanied by a sudden lowering of surface pressure; (ii) Precipitable water tendency (DPWV) becomes increasingly small moving from half-hour to monthly time scale, but not negligible compared with both the moisture flux divergence div ( Q ) and the imbalance between actual evapotranspiration and precipitation ( E – P ), especially during spring and fall; (iii) GPS observations, jointly with other meteorological data, can provide an accurate estimate of the imbalance ( E – P ) that is of interest for drought assessment, and of the terrestrial water storage rate of change that is known to be difficult to measure; (iv) the availability of on-site precipitation observations allows the computation of precipitation efficiency, which is a key parameter for estimating the water availability in a given area and monitoring dry/wet spells. It appears that for a comprehensive monitoring of a river basin, a GPS network that encloses the area of concern, equipped with meteorological ground sensors, is suitable and desirable.

Two types of persistent extreme weather events, the cold–wet spell (CWS) and the persistent wet-freezing event (PWFE), are defined by considering the persistence of both extreme low temperature (ELT) and precipitation. Regional CWS and PWFE are identified based on temporal persistence and spatial contiguity of single-station-based CWS event and PWFE, respectively. Relevant factors are further discussed to reveal the features of spatial distribution and temporal variability of such events. The results indicate that: (1) station-based CWSs are mostly observed in southern China, especially in eastern part of southwest China and south China. PWFEs are relatively frequently observed immediate south of middle reach of the Yangtze River. Both CWS and PWFE of longer duration are frequently observed in the northern part of the Yunnan–Guizhou Plateau. Further analyses indicate that the occurrence of these events in southern China is positively related to elevation. (2) A total of 48 regional CWSs and 21 regional PWFEs are identified during cold season over 1951–2011 in China. The long-lasting ELT and rainy (snowy)/freezing condition render the event in southern China in 2008, the most severe one in the last five decades. (3) Precipitation is the limitation condition for the occurrence of CWS and PWFE in northern China, while ELT is the dominant factor for CWS and PWFE in southern China.

We employ a large ensemble of Regional Climate Models (RCMs) from the COordinated Regional-climate Downscaling EXperiment to explore two questions: (1) what can we know about the future precipitation characteristics over Africa? and (2) does this information differ from that derived from the driving Global Climate Models (GCMs)? By taking into account both the statistical significance of the change and the models’ agreement on its sign, we identify regions where the projected climate change signal is robust, suggesting confidence that the precipitation characteristics will change, and those where changes in the precipitation statistics are non-significant. Results show that, when spatially averaged, the RCMs median change is usually in agreement with that of the GCMs ensemble: even though the change in seasonal mean precipitation may differ, in some cases, other precipitation characteristics (e.g., intensity, frequency, and duration of dry and wet spells) show the same tendency. When the robust change (i.e., the value of the change averaged only over the land points where it is robust) is compared between the GCMs and RCMs, similarities are striking, indicating that, although with some uncertainty on the geographical extent, GCMs and RCMs project a consistent future. Potential added value of downscaling future climate projections (i.e., non-negligible fine-scale information that is absent in the lower resolution simulations) is found for instance over the Ethiopian highlands, where the RCM ensemble shows a robust decrease in mean precipitation in contrast with the GCMs results. This discrepancy may be associated with the better representation of topographical details that are missing in the large scale GCMs. The impact of the heterogeneity of the GCM–RCM matrix on the results has been also investigated; we found that, for most regions and indices, where results are robust or non-significant, they are so independently on the choice of the RCM or GCM. However, there are cases, especially over Central Africa and parts of West Africa, where results are uncertain, i.e. most of the RCMs project a statistically significant change but they do not agree on its sign. In these cases, especially where results are clearly clustered according to the RCM, there is not a simple way of subsampling the model ensemble in order to reduce the uncertainty or to infer a more robust result.

Daily rain gauge data over Europe for the period from 1950 to 2009 were used to analyze changes in the duration of wet and dry spells. The duration of wet spells exhibits a statistically significant growth over northern Europe and central European Russia, which is especially pronounced in winter when the mean duration of wet periods increased by 15%–20%. In summer wet spells become shorter over Scandinavia and northern Russia. The duration of dry spells decreases over Scandinavia and southern Europe in both winter and summer. For the discrimination between the roles of a changing number of wet days and of a regrouping of wet and dry days for the duration of the period, the authors suggest a fractional truncated geometric distribution. The changing numbers of wet days cannot explain the long-term variability in the duration of wet and dry periods. The observed changes are mainly due to the regrouping of wet and dry days. The tendencies in duration of wet and dry spells have been analyzed for a number of European areas. Over the Netherlands both wet and dry periods are extended in length during the cold and the warm season. A simultaneous shortening of wet and dry periods is found in southern Scandinavia in summer. Over France and central southern Europe during both winter and summer and over the Scandinavian Atlantic coast in summer, opposite tendencies in the duration of wet and dry spells were identified. Potential mechanisms that might be responsible for the changing durations of wet and dry periods and further perspectives are discussed.

The South Asian summer monsoon strongly modulates regional temperature and humidity. While extreme dry heat peaks in the pre‐monsoon season, recent literature suggests that extreme humid heat can continue to build throughout the monsoon season. Here we explore the influence of monsoon onset and subseasonal precipitation variability on the occurrence of extreme wet bulb temperatures (Tw) across South Asia. We find that extreme Tw events often occur on rainy days during the monsoon season. However, the influence of precipitation on Tw varies with the background climatology of surface specific humidity. In climatologically drier areas, positive Tw anomalies tend to occur when precipitation increases due to either early onset or wet spells during the monsoon. In contrast, in climatologically humid areas, positive Tw anomalies occur during periods of suppressed precipitation, including both delayed onset and dry spells during the monsoon. Plain Language Summary The combination of high heat and humidity poses greater risks to human health, productivity, and well‐being relative to elevated temperatures alone. South Asia has already experienced some of the most extreme humid heat observed on Earth. Typically, the highest temperatures in South Asia occur during the pre‐monsoon season in March‐May. While the precipitation and cloudiness associated with the summer monsoon reduce extreme air temperatures, the increased humidity can contribute to the occurrence of extreme humid heat events. Our research finds that a majority of extreme Tw events across South Asia happen on rainy days during the monsoon season. This is especially true for regions where surface humidity is typically low during the monsoon season, and Tw tends to be higher during heavier than usual precipitation spells and during years when the monsoon season starts earlier in the calendar year. In regions with high background surface humidity, however, Tw is more intense when there is less precipitation than usual or when the monsoon onset is delayed. These results help to identify additional times with high risk of heat stress for outdoor workers, and provide a new way of understanding how monsoon variations influence local humid heat. Key Points In contrast to dry heat, most extreme wet bulb temperature events in South Asia take place on rainy days during the monsoon season Local background specific humidity determines whether wet bulb temperatures are intensified by enhanced or suppressed precipitation Baseline moisture availability also influences whether early or delayed monsoon onset intensifies wet bulb temperature anomalies