Analysis of space–time patterns of rainfall events during 1996–2008 in Yilan County (Taiwan)

Stochastic Environmental Research and Risk Assessment - Understanding local precipitation patterns is essential to water resource management and flood mitigation. Precipitation patterns can vary in...     

Trends and discontinuities in regional rainfall of West and Central Africa: 1951–1989

Abstract

Standardized regional mean annual rainfall series are analysed over the period 1951–1989 from a data set of 891 rainfall stations which covers 23 countries of West and Central Africa. Missing values are estimated by using regionalized indexes computed on the basis of a morpho-climatic delimitation of 44 homogeneous climatic units. Searches for statistical discontinuities in rainfall series show no discontinuity for most units of Central Africa. For several units of West Africa the first discontinuity occurs at the end of the 1950s. The main discontinuity period occurs between 1968 and 1970, followed by a second one at the beginning of the 1980s. Rainfall deficit is greater north of 10°N, and is also important in the Guinean Mountains and on the northern coast of the Gulf of Guinea, west of the Atakora Mountains. Regions leeward of mountainous areas experienced moderate rainfall decrease.     

Evaluation of the applicability of multiple drought indices in the core zone of “westerlies-dominated climatic regime”

Drought indices are frequently used to measure the intensity, start and end of droughts. However, the performances of these indices depend on regions and the type of droughts. Therefore, it is necessary to evaluate whether these indices are applicable for a given region. This study evaluated the ability of the self-calibrating Palmer Drought Severity Index(sc PDSI), the Standardized Precipitation Evapotranspiration Index(SPEI), and the Standardized Moisture Anomaly Index(SZI) to describe the dry...     

Basin-scale analysis of rainfall and runoff in Peru (1969–2004): Pacific,Titicaca and Amazonas drainages

Abstract

We present a procedure for estimating Q95 low flows in both gauged and ungauged catchments where Q95 is the flow that is exceeded 95% of the time. For each step of the estimation procedure, a number of alternative methods was tested on the Austrian data set by leave-one-out cross-validation, and the method that performed best was used in the final procedure. To maximise the accuracy of the estimates, we combined relevant sources of information including long streamflow records, short streamflow records, and catchment characteristics, according to data availability. Rather than deriving a single low flow estimate for each catchment, we estimated lower and upper confidence limits to allow local information to be incorporated in a practical application of the procedure. The components of the procedure consist of temporal (climate) adjustments for short records; grouping catchments into eight seasonality-based regions; regional regressions of low flows with catchment characteristics; spatial adjustments for exploiting local streamflow data; and uncertainty assessment. The results are maps of lower and upper confidence limits of low flow discharges for 21 000 sub-catchments in Austria.     

Improvement and comparison of the rainfall–runoff methods in SWAT at the monsoonal watershed of Baocun,Eastern China

ABSTRACT

A new physics-based rainfall–runoff method of the Soil and Water Assessment Tool (SWAT) was developed, which integrates a water balance (WB) approach with the variable source area (WB-VSA). This approach was further compared with four methods—soil-water-dependent curve number (CN-Soil), evaporation-dependent curve number (CN-ET), Green and Ampt equation (G&A) and WB—in a monsoonal watershed, Eastern China. The regional sensitivity analysis shows that volumetric efficiency coefficient (VE) with river discharges is sensitive to the most parameters of all approaches. The results of model calibration against VE demonstrate that WB-VSA is the most accurate owing to its reflection of the spatial variation of runoff generation as affected by topography and soil properties. Other methods can also mimic baseflow well, but the G&A and CN-ET simulate floods much worse than the saturation excess runoff approaches (WB-VSA, WB and CN-Soil). Meanwhile, CN-Soil as an empirical method fails to simulate groundwater levels. By contrast, WB-VSA captures them best.

Editor M.C. Acreman; Associate editor S. Kanae     

Impairment of radio wave signal by rainfall on fixed satellite service on earth–space path at 37 stations in Nigeria

This study investigates the effect of rainfall on horizontally polarized radio waves for fixed satellite service at Ku, Ka and V bands for links to the recently launched Nigeria Communication Satellite one (NigComSat-1), for annual time availabilities of 99–99.99% in an average year for 37 stations in Nigeria. The results obtained at Ku-band downlink shows that 99.99% availability is possible in all the 37-stations in Nigeria. At Ka-band downlink the results also show that only 99.9% availability is practicable in all the 37 stations in Nigeria. At V-band downlink, 99.99% availability is also not possible in all the 37 stations in Nigeria. An availability level of 99.9% is only practicable in the North–West (NW) and North–East (NE) regions, where the attenuation is between 14 and 17.9 dB. Total fade out of signals during rainfall are probable in the South–South (SS), South–East (SE), South–West (SW) and Middle–Belt (MB) regions at 99.9% availability.     

Characteristics of recent tectonic stress field in Jiashi, Xinjiang and adjacent regions

Introduction The Pamirs region where Jiashi is located is one of the most active regions of continental plate dynamics in China. Frequent earthquakes here, especially several strong earthquakes oc- curred in 1997 and 2003, have provided excellent conditions for studying the tectonic stress field in this region and a large number of results (GAO and WEN, 2000; GAO et al, 2004; XU, 2001; ZHOU et al, 2001) have been obtained. Although different methods and data were used, under- standings …     

Sensitivity and fuzzy uncertainty analyses in the determination of SCS-CN parameters from rainfall–runoff data

Spatial and seasonal variations of curve number (CN) and initial abstraction ratio (λ) in a watershed can result in inaccurate runoff volume estimations when using the US Natural Resources Conservation Service (SCS-CN) method with constant values for these parameters. In this paper, parameters of CN and λ are considered as calibration parameters and the sensitivity of estimated runoff to these parameters using the SCS-CN method is scrutinized. To incorporate the uncertainty associated with CN and λ, fuzzy linear regression (FLR) is applied to derive the relationships of CN and λ with rainfall depth (P) by employing a large dataset of storm events from four watersheds in Iran. Results indicate that the proposed approach provides more accuracy in estimation of runoff volume compared to the SCS method with constant values of CN and λ, and gives a straightforward technique for evaluating the hydrological effects of CN, λ, and P on runoff volume.     

Reservoir induced seismicity in the Koyna–Warna region,India: Overview of the recent results and hypotheses

The state of the art in the geological and geophysical study of the region of Koyna and Warna water reservoirs is reviewed. The probable geodynamical factors of induced seismicity are discussed. The detailed geophysical surveys, satellite geodetic data, and time history of the seismicity in the region reveal a complicated pattern of the structure and recent geodynamics of the region. The existing data suggest that the induced seismicity is here most likely to be caused by the regional (intraplate) stresses driving the displacements along the orthogonal network of the faults whose strength has dropped and continues decreasing due to the reservoir impoundment and operation processes. The evolution of the seismicity which started immediately after the rapid filling of the Koyna reservoir in the region of the dam, then rapidly expanded southwards and eventually became concentrated in the region of the subsequently constructed Warna reservoir shows that seismic events can be initiated by a number of factors whose contributions may vary with time. The key ones among them include reservoir loading and its seasonal variations; water saturation of the faults which guide the propagation of the front of fracture, increased permeability, and, probably, mineral transformations (hydrolysis) under the water level fluctuations in the reservoirs; and displacement of the front of the high pore pressure down to the main source zone of the earthquakes at a depth of 6–8 km. Based on the analysis presented in the paper, we outline the directions of the future research aimed at studying the nature and dynamics of induced seismicity in the region of large water reservoirs.     

Hydrological impact of forest-fire from paired-catchment and rainfall–runoff modelling perspectives

Abstract

This study deals with the Rimbaud catchment, a sub-catchment within the Réal Collobrier hydrological observatory in southeastern France, managed by Irstea since 1966. This observatory suffered a wildfire in 1990. Because of the dense network of streamgauges and raingauges available, this site provides a unique opportunity to test and compare two types of analysis, one based on paired catchments and the other a rainfall–runoff model, used to assess the hydrological impact of forest fire. In the present case, more than 20 years of pre-fire and post-fire data are available. We compare the ability of the two approaches to detect gradual changes at a daily time step. This case study illustrates how natural climatic variability (here a long drought which preceded the wildfire) can make the identification of hydrological changes extremely difficult.     

The spatial–temporal variation of dry and wet periods in Iran based on comparing SPI and RDI indices

Drought is a natural hazard which can cause harmful effects on water resources. To monitor drought, the use of an indicator and determination of wet and dry period trend seem to have an important role in quantifying the drought analysis. In this paper, in addition to the comparison of Reconnaissance Drought Index (RDI) and Standardized Precipitation Index (SPI), based on the most appropriate probability distribution function, it was tried to examine the trends of dry and wet periods based on the mentioned indices. Accordingly, the meteorological data of 30 synoptic stations in Iran (1960–2014) was used and the trend was analyzed using the Mann–Kendall test by eliminating the effect of any significant autocorrelation coefficients at 95% confidence level (modified Mann–Kendall). Comparing results between the time series of RDI and SPI drought indices based on statistical indicators (RMSE?<?0.434, R²?>?0.819 and T-statistic?<?0.419) in all studied stations revealed that the behavior of the two indices was roughly the same and the difference between them was not significant. The trend analysis results of RDI and SPI indices based on modified Mann–Kendall test showed that the variation of dry and wet periods was decreasing in most of the studied stations (five cases were significant). In addition, the results of the trend line slope of dry and wet periods related to the drought indices in the studied area indicated that the slope was negative for SPI and RDI indices in 70% and 50% of stations, respectively.     

Multi-decadal changes in the relationships between rainfall characteristics and debris-flow occurrences in response to gully evolution after the 1990–1995 Mount Unzen eruptions

Explosive volcanic eruptions can cause long-term landscape change, leading to increased sediment discharge that continues after the cessation of the eruptions. During the period 1990–1995, eruptions of Mount Unzen, Japan, generated large amounts of pyroclastic material, resulting in 57 debris-flow events during 1991–2018. To investigate changes in the relationships between rainfall characteristics and debris-flow occurrence, we conducted the following: geometric analysis of two gullies (i.e., debris-flow initiation zones) using LiDAR (light detection and ranging)-generated 1 m DEMs (digital elevation models); rainfall analysis, based on the relationship between rainfall duration and mean intensity (i.e., considering the intensity–duration, or ID, threshold); and debris-flow monitoring during 2016–2018. Since 1991, rainfall runoff has caused erosion of the supplied pyroclastic material, generating a channel network consisting of incised gullies. With sufficient rainfall, debris flows formed, accompanied by further gully erosion; this resulted in both vertical and lateral adjustments of the cross-sectional geometry. In the two decades since the eruptions ceased, readily mobilized pyroclastic material has become scarce as the gullies have adjusted to local hydrographic conditions. At the same time, the infiltration capacity of the volcanic flank has increased, reducing the capacity for overland flow. As a result, since 2000, rainfall events with intensities above the ID threshold have occurred; however, the lack of sediment supplied by the gullies appears to have hindered the occurrence and development of debris flows. This suggests that debris flows in volcanically perturbed landscapes may occur at lower rainfall thresholds as long as the corresponding upland channels are evolving as a result of intense overland flow. However, as such channels evolve towards equilibrium geometries, the frequency of debris flows decreases in response to the reduction in sediment availability.     

Comparison of an artificial neural network and a conceptual rainfall–runoff model in the simulation of ephemeral streamflow

ABSTRACT

The rainfall–runoff process is governed by parameters that can seldom be measured directly for use with distributed models, but are rather inferred by expert judgment and calibrated against historical records. Here, a comparison is made between a conceptual model (CM) and an artificial neural network (ANN) for their ability to efficiently model complex hydrological processes. The Sacramento soil moisture accounting model (SAC-SMA) is calibrated using a scheme based on genetic algorithms and an input delay neural network (IDNN) is trained for variable delays and hidden layer neurons which are thoroughly discussed. The models are tested for 15 ephemeral catchments in Crete, Greece, using monthly rainfall, streamflow and potential evapotranspiration input. SAC-SMA performs well for most basins and acceptably for the entire sample with R² of 0.59–0.92, while scoring better for high than low flows. For the entire dataset, the IDNN improves simulation fit to R² of 0.70–0.96 and performs better for high flows while being outmatched in low flows. Results show that the ANN models can be superior to the conventional CMs, as parameter sensitivity is unclear, but CMs may be more robust in extrapolating beyond historical record limits and scenario building.

EDITOR M.C. Acreman; ASSOCIATE EDITOR not assigned     

GPS monitoring of recent crustal movements in Kamchatka and the Commander Islands during 1997–2007

This is a review of the geodetic monitoring of the horizontal component of recent crustal movements (RCMs) in Kamchatka and the Commander Islands for the period 1979–2007. Examples are provided of the RCMs recorded in Kamchatka and the Commander Islands for the period 1997–2007 by the Kamchatka regional GPS network (KAMNET) set up by workers at the Kamchatka Branch of the RAS Geophysical Service (KB GS RAS) in collaboration with the Institute of Volcanology and Seismology of the Far East Division of the Russian Academy of Sciences to study the geodynamic processes that are occurring in the Kamchatka subduction zone. An interpretation of examples of recorded RCMs is given.     

Space–Time Analysis of Hydrochemical Composition and Pollution of Water in the Northern Dvina Basin

Water Resources - Water quality dynamics along the Northern Dvina River is analyzed under the conditions of anthropogenic impact. Overall, river water is classified as very polluted. The cases of...     

Characteristics of Changes in the Ozone Content in the Upper Stratosphere over Moscow during the Cold Half-Years of 2014–2015 and 2015–2016

Geomagnetism and Aeronomy - The results of ground-based microwave measurements of the stratospheric ozone profiles over Moscow during the cold half-years of 2014–2015 and 2015–2016 are...     

Spatial and temporal variations in rainfall erosivity during 1960–2005 in the Yangtze River basin

Water resources and soil erosion are the most important environmental concerns in the Yangtze River basin, where soil erosion and sediment yield are closely related to rainfall erosivity. The present study explores the spatial and temporal changing patterns of the rainfall erosivity in the Yangtze River basin of China during 1960–2005 at annual, seasonal and monthly scales. The Mann–Kendall test is employed to detect the trends during 1960–2005, and the T test is applied to investigate possible changes between 1991–2005 and 1960–1990. Meanwhile the Rescaled Range Analysis is used for exploring future trend of rainfall erosivity. Moreover the continuous wavelet transform technique is using studying the periodicity of the rainfall erosivity. The results show that: (1) The Yangtze River basin is an area characterized by uneven spatial distribution of rainfall erosivity in China, with the annual average rainfall erosivity range from 131.21 to 16842 MJ mm ha^?1 h^?1. (2) Although the directions of trends in annual rainfall erosivity at most stations are upward, only 22 stations have significant trends at the 90 % confidence level, and these stations are mainly located in the Jinshajiang River basin and Boyang Lake basin. Winter and summer are the seasons showing strong upward trends. For the monthly series, significant increasing trends are mainly found during January, June and July. (3) Generally speaking, the results detected by the T test are quite consistent with those detected by the Mann–Kendall test. (4) The rainfall erosivity of Yangtze River basin during winter and summer will maintain a detected significant increasing trend in the near future, which may bring greater risks to soil erosion. (5) The annual and seasonal erosivity of Yangtze River basin all have one significant periodicity of 2–4 years.