Shouraseni Sen Roy

Rapid urbanization and changes in spatiotemporal characteristics of precipitation in Beijing metropolitan area

This study investigates changes in temporal trends and spatial patterns of precipitation in Beijing over the last six decades. These changes are discussed in the context of rapid urbanization and the growing imbalance between water supply and demand in Beijing. We observed significant decreases in precipitation amounts from 1950 to 2012, with the annual precipitation decreasing by 32% at a decadal rate of 28.5 mm. In particular, precipitation decrease is more pronounced in the summer and warm seasons when water use is at its seasonal peak. We further analyzed hourly precipitation data from 43 rain gauges between 1980 and 2012 to examine the spatiotemporal characteristics of both precipitation amount and intensity across six distinct subregions in Beijing. No significant spatial variations in precipitation changes were identified, but slightly greater amounts of precipitation were noted in the urban areas (plains) than in the surrounding suburbs (mountains), due to the effect of urbanization and topography. Precipitation intensity has increased substantially, especially at the hourly duration, as evidenced by the more frequent occurrence of extreme storms. The observed decreased water availability and the increase in extreme weather events require more integrated water management, particularly given the expectation of a warmer and more variable climate, the continued rapid growth of the Beijing metropolis, and the intensifying conflict between water supply and demand.

The Impacts of Enso, PDO, and Local SSTS on Winter Precipitation in India

Monthly precipitation data are assembled to analyze the impact of global teleconnections, namely ENSO, PDO, and local sea surface temperatures (SSTs) on winter rainfall across the Indian subcontinent, from 1925 to 1998. Canonical correlation analysis reveals one statistically significant vector for the precipitation occurring over the subcontinent and one for the predictor variables. The results of the analysis indicated a negative relationship between winter precipitation and both ENSO and PDO indices. Most of peninsular Indias precipitation, extending into the central plateau region, exhibited a negative correlation with SSTs around the mainland, with the eastern part of the Arabian Sea and adjacent Indian Ocean exhibiting a relatively higher negative correlation. Precipitation in the northeastern part of the country exhibits a positive correlation with the local SSTs. The overall variance explained by the selected set of predictor variables accounts for 12.07% of the total variance in winter precipitation taking place across India. The results of the study will be useful for greater efficiency in the forecasting of winter precipitation.

An Analysis of Local Spatial Temperature Patterns in The Delhi Metropolitan Area

The present study focuses on spatial patterns of urban heat island (UHI) development within the rapidly changing urban landscape of the Delhi Metropolitan Region (DMR). To determine the role of local environmental factors in the shaping of microclimatic conditions, automated weather sensors were installed at 13 sites for a one-year period from May 2007 to June 2008. The results indicate significant differences in observed near-surface temperatures among the different stations. The UHI effect was more pronounced in the late afternoon and nocturnal hours. The highest temperatures are observed in the northern and western sections of the study area, which overlap with high-density residential and industrial land uses. Furthermore, these areas also experienced extreme high temperatures of prolonged duration during the daytime, increasing heat-related risks in these areas. At the seasonal level, the greatest differences in temperatures were observed during the summer, likely due to the predominantly clear sky conditions. However, areas of higher temperatures were relatively localized during the cooler months of the year.

Analysis of Diurnal Patterns in Winter Precipitation across the Conterminous United States

Abstract Hourly winter (November–March) precipitation data were assembled for nearly 5000 stations in the conterminous United States over the period 1948–98. Despite a potential observation bias in the 24th hour, a general tendency for winter precipitation events was found to occur more frequently near sunrise than for any other time of the day. Based on the standardized amplitude of the first harmonic wave, the pattern is most pronounced in Texas and in an area surrounding Colorado and Wyoming. The pattern also appears significant in the southeastern United States and in northern California based on the variance explained by the first harmonic fit. It is suggested that the diurnal patterns seen in the conterminous United States are related to increased relative humidity values occurring near sunrise and increased wind speeds in the warm sector of cyclonic storms.

Spatial variations in the diurnal patterns of winter precipitation in India.

The present study focuses on spatial patterns of diurnal variability in winter precipitation across the Indian subcontinent. Hourly precipitation data during the months of January and February from 1980 to 2002 were procured for 80 stations spread across the subcontinent. The methodology consisted of calculation of the first harmonics by harmonic analysis for three variables that included frequency, total amount, and intensity of precipitation events. There were substantial variations in the strength of the diurnal cycle prevailing over the subcontinent, with most of the peninsular region and eastern part of the northern Gangetic Plain showing relatively stronger diurnal cycles. The variance explained by the first harmonic was significant at the 90% confidence level for larger parts of the peninsular region and northern plains. The weakest patterns were observed in the interior of the continent over central India. The times of maximum for hourly frequency, total amount, and intensity of precipitation were predominantly during the latter half of the 24–hour period, during late evening hours to just before sunrise hours. This was due to the enhanced warm front lifting during the late night to early morning hours as a result of nighttime inversions in the warm sector. Further, along the foothills of the Himalayas, the times of maximum were observed during predawn hours just before sunrise, caused by the downslope movement of katabatic winds and their convergence with the cyclonic storms in the low-lying areas, leading to enhanced precipitation. Along the west coast, the times of maxima were also concentrated in the midnight to early-morning hours due to the convergence of inland moving seas breeze fronts with the northeast trades.

Trends in Extreme Precipitation Indices in Iran: 1951–2007

We investigate trends in extreme precipitation in Iran for 1951–2007 using the recently released APHRODITE daily rainfall time series. We find that seven different indices of extreme precipitation all show an upward trend through the study period. The seven different precipitation indices include annual precipitation total, number of days above a certain threshold, maximum precipitation received over a certain period of time, maximum one-day precipitation, and number of days with precipitation above the 90th percentile. A principal components analysis reveals one eigenvector explaining much of the variance in the seven indices and reveals that this component exhibits a strong upward trend for the whole of Iran. On a regional level, we find that the upward trend in extreme precipitation has a strong southwest-to-northeast gradient across the country for all the indices. We repeated all the analyses for 42 stations across the country to compare with the results from the gridded data; trends in extreme rainfall generated from the station data compare favorably with the results from the APHRODITE daily rainfall time series thereby reinforcing the robustness of our conclusions.

Patterns and Variability of Summer NDVI in Response to Climate Variables in Minnesota

This study examines the relationship between summer season NDVI and local-level climate variables, consisting of precipitation and temperature, in Minnesota from 1990 to 1997 using Geographically Weighted Regression (GWR). In comparison to traditional global techniques of Ordinary Least Squared (OLS) regression, there is a substantial improvement in the analysis using GWR. The overall relationship among the different variables was broadly consistent for the diverse types of land uses across the state. The spatial patterns of the association in the form of regression coefficients were not very consistent over the years as a result of interannual variations in the local climate.

Spatial Patterns of Larceny and Aggravated Assault in Miami–Dade County, 2007–2015

The combination of crime mapping and geospatial analysis methods has enabled law enforcement agencies to develop more proactive methods of targeting crime-prone neighborhoods based on spatial patterns, such as hot spots and spatial proximity to specific points of interest. In this article, we investigate the spatial and temporal patterns of the neighborhood crimes of aggravated assault and larceny in 297 census tracts in Miami–Dade County from 2007 to 2015. We use emerging hot spot analysis (EHSA) to identify the spatial patterns of emerging, persistent, continuous, and sporadic hot spots. In addition, we use geographically weighted regression to analyze the spatial clustering effects of sociodemographic variables, poverty rate, median age, and ethnic diversity. The hot spots for larceny are much more diffused than those for aggravated assaults, which exhibit clustering in the north over Liberty City and Miami Gardens and in the south near Homestead, and the ethnic heterogeneity index has a moderate and positive effect on the incidence of both larceny and aggravated assaults. The findings suggest that law enforcement can better target prevention programs for violent versus property crime using geospatial analyses. Additionally, the ethnic concentration of neighborhoods influences crime differently in neighborhoods of different socioeconomic status, and future studies should account for spatial patterns when estimating conventional regression models.

Spatial patterns of off-the-system traffic crashes in Miami–Dade County, Florida, during 2005–2010

ABSTRACT Objective: The objective of this study is to analyze the spatial distribution of the vehicles involved in crashes in Miami–Dade County. In addition, we analyzed the role of time of day, day of the week, seasonality, drivers’ age in the distribution of traffic crashes. Method: Off-the-system crash data acquired from the Florida Department of Transportation during 2005–2010 were divided into subcategories according to the risk factors age, time of day, day of the week, and travel season. Various spatial statistics methods, including nearest neighbor analysis, Getis-Ord hot spot analysis, and kernel density analysis revealed substantial spatial variations, depending on the subcategory in question. Results: Downtown Miami and South Beach showed up consistently as hotspots of traffic crashes in all subcategories except fatal crashes. However, fatal crashes were concentrated in residential areas in inland areas. Conclusion: This understanding of patterns can help the county target high-risk areas and help to reduce crash fatalities to create a safer environment for motorists and pedestrians.

Diurnal variation in the initiation of rainfall over the Indian subcontinent during two different monsoon seasons of 2008 and 2009

In the present study, the diurnal variations in the time of initiation of rainfall, during two contrasting monsoon seasons of 2008 (below normal) and 2009 (normal) over the Indian subcontinent and surrounding oceanic areas has been analyzed. Harmonic analysis was used to detect the spatial variation of the diurnal cycle of the time of initiation of rainfall, as obtained at half-hourly intervals from the Kalpana 1 satellite. In general, the diurnal cycle in the time of initiation is strongest in regions where convective clouds are predominant, while it is weaker in regions where the clouds are predominantly stratiform with long-lived medium to high cloud cover. In the interior of the subcontinent, the time of maximum mainly occurred in the afternoon to evening hours, with a distinct southeast to northwest gradation. Substantial spatial variations were detected in the diurnal patterns between a normal and below normal monsoon years. Spatially, rainfall is initiated later in 2009 compared to 2008 over most of the interior of the Indian subcontinent. The most distinct difference was observed over the core monsoon region in central India, where the diurnal patterns were stronger in 2009 compared to 2008. On the other hand, over the oceans surrounding the Indian subcontinent, the initiation times are generally earlier in 2009.