Joint Global Change Research Institute

About: Joint Global Change Research Institute is a facility organization based out in Riverdale Park, Maryland, United States. It is known for research contribution in the topics: Greenhouse gas & Climate change. The organization has 197 authors who have published 934 publications receiving 62390 citations.

100 years of data is not enough to establish reliable drought thresholds

Abstract: Drought research customarily uses statistics collected over a reference period to establish a threshold for declaring a region to be in a drought, or to estimate baseline return periods. Often these statistics involve quantile values from the tails of the distribution of reference period observations, such as 10th or even 1st percentile values. The length of the reference period is dictated by the available record length; often it is no longer than 50–100 years. Depending on the purpose for which the drought study is intended, the unit of time used as the averaging period for the hydrologic or meteorologic variables of interest is often as small as one month. In this circumstance, percentile values are each based on at most 100 data points. We show here that the statistical uncertainty resulting from these small sample sizes for estimating the threshold value is sufficient to compromise many types of analysis. We provide formulae for calculating the statistical uncertainties caused by limited record lengths and for estimating the record length needed to achieve a specified level of accuracy in an analysis. Our results show that datasets of 100 years or less are approximately 1/10 the length needed to achieve the level of reliability required for many applications. We also summarize options for augmenting the historical record when the existing record length is not long enough to support analysis at the desired level of accuracy.

Spatial and Temporal Patterns of Wetland Cover Changes in East Kolkata Wetlands, India from 1972 to 2011

Abstract: Land use and land cover change has a slow but prolonged impact on various aspects of environment on local, regional and global scales. In developing countries especially population pressure and food demand have compelled conversion of wetlands to built-up and agricultural lands. One such unique example is the East Kolkata Wetlands (EKWs) located on the eastern fringes of Kolkata City in India where such land cover change is very intense and rapid. In this study, wetland conversions in EKWs from 1972 to 2011 were analyzed with four Landsat images using the Geographic Object-Based Image Analysis (GeOBIA) and a post-classification comparison. Results suggested that wetland areas decreased by 17.9 percent during the study period. The western part of the wetlands saw the maximum conversion of wetlands to built-up areas with time, whereas the east and south experienced more of wetlands to agricultural and other land conversions