Threshold exceedances and cumulative ozone exposure indices at tropical suburban site

This study provides the first analysis of threshold exceedances and cumulative ozone exposure indices from Pune, a tropical suburban site in India. We used the directives on ozone pollution in ambient air provided by the United Nations Economic Commission for Europe, and by the World Health Organization to assess the air quality from in situ measurements of surface ozone (during the years 2003-2006). We find that the exposure-plant response index (Accumulated exposure Over a Threshold of 40 ppb (AOT40)) and target values for protection of human health (8-h > 60 ppb) are regularly surpassed. This is a concern for agricultural and human health. Air-mass classification based on back-air trajectories shows that the excess of AOT40 values is quite plausibly due to long-range transport of background ozone and its precursors to the measurement site

Precipitation in a warming world: Assessing projected hydro-climate changes in California and other Mediterranean climate regions.

In most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures. In California, however, projections of changes in annual precipitation are inconsistent. Analysis of daily precipitation in 30 GCMs reveals patterns in projected hydrometeorology over each of the five MedClm regions globally and helps disentangle their causes. MedClim regions, except California, are expected to dry via decreased frequency of winter precipitation. Frequencies of extreme precipitation, however, are projected to increase over the two MedClim regions of the Northern Hemisphere where projected warming is strongest. The increase in heavy and extreme precipitation is particularly robust over California, where it is only partially offset by projected decreases in low-medium intensity precipitation. Over the Mediterranean Basin, however, losses from decreasing frequency of low-medium-intensity precipitation are projected to dominate gains from intensifying projected extreme precipitation. MedClim regions are projected to become more sub-tropical, i.e. made dryer via pole-ward expanding subtropical subsidence. California's more nuanced hydrological future reflects a precarious balance between the expanding subtropical high from the south and the south-eastward extending Aleutian low from the north-west. These dynamical mechanisms and thermodynamic moistening of the warming atmosphere result in increased horizontal water vapor transport, bolstering extreme precipitation events

Precipitation regime change in Western North America: The role of Atmospheric Rivers.

Daily precipitation in California has been projected to become less frequent even as precipitation extremes intensify, leading to uncertainty in the overall response to climate warming. Precipitation extremes are historically associated with Atmospheric Rivers (ARs). Sixteen global climate models are evaluated for realism in modeled historical AR behavior and contribution of the resulting daily precipitation to annual total precipitation over Western North America. The five most realistic models display consistent changes in future AR behavior, constraining the spread of the full ensemble. They, moreover, project increasing year-to-year variability of total annual precipitation, particularly over California, where change in total annual precipitation is not projected with confidence. Focusing on three representative river basins along the West Coast, we show that, while the decrease in precipitation frequency is mostly due to non-AR events, the increase in heavy and extreme precipitation is almost entirely due to ARs. This research demonstrates that examining meteorological causes of precipitation regime change can lead to better and more nuanced understanding of climate projections. It highlights the critical role of future changes in ARs to Western water resources, especially over California

Projected changes of rainfall seasonality and dry spells in a high greenhouse gas emissions scenario

In this diagnostic study we analyze changes of rainfall seasonality and dry spells by the end of the twenty-first century under the most extreme IPCC5 emission scenario (RCP8.5) as projected by twenty-four coupled climate models contributing to Coupled Model Intercomparison Project 5 (CMIP5). We use estimates of the centroid of the monthly rainfall distribution as an index of the rainfall timing and a threshold-independent, information theory-based quantity such as relative entropy (RE) to quantify the concentration of annual rainfall and the number of dry months and to build a monsoon dimensionless seasonality index (DSI). The RE is projected to increase, with high inter-model agreement over Mediterranean-type regions---southern Europe, northern Africa and southern Australia---and areas of South and Central America, implying an increase in the number of dry days up to 1Â month by the end of the twenty-first century. Positive RE changes are also projected over the monsoon regions of southern Africa and North America, South America. These trends are consistent with a shortening of the wet season associated with a more prolonged pre-monsoonal dry period. The extent of the global monsoon region, characterized by large DSI, is projected to remain substantially unaltered. Centroid analysis shows that most of CMIP5 projections suggest that the monsoonal annual rainfall distribution is expected to change from early to late in the course of the hydrological year by the end of the twenty-first century and particularly after year 2050. This trend is particularly evident over northern Africa, southern Africa and western Mexico, where more than 90% of the models project a delay of the rainfall centroid from a few days up to 2Â weeks. Over the remaining monsoonal regions, there is little inter-model agreement in terms of centroid changes

Mapping and spatial-temporal assessment of gully density in the Middle Volga region, Russia

© 2018 John Wiley & Sons, Ltd. A large-scale mapping of gully density was carried out for the Middle Volga region of the Russian Plain (188 000 km2) based on the interpretation of aerial photographs (scale 1:17 000; surveys undertaken during 1956–1970). In addition, spatial-temporal dynamic of gully density were assessed for some parts of the study area (the Udmurt Republic and the Mesha and Ulema River basins of Tatarstan), based on the interpretation of aerial photographs (survey 1986–1991) and high resolution satellite images (2012–2015). Information on factors potentially controlling gully formation and development were collected and a geographic information system (GIS) analysis was conducted. Results show the strong development of gullies in the study area over the 1956–1970 period with an average gully density of 0.21 km km−2. For the Udmurt region, we found that gully densities varied little in the period 1956–1986, during which the total active gully length reduced with only 2%. This period was characterized by low variable climatic conditions and a stable fraction of arable land with a relatively continuous crop rotation system. However, gully dynamics seems to have changed more strongly during recent decades. We found a strong (order of magnitude) reduction in active gully density for the period 2010–2015 as compared to 1986–1991. The main reason for this is likely the increasing winter air temperatures. This leads to a significant reduction in surface runoff during spring as a result of snowmelt. Nonetheless, in some regions (i.e. the Udmurt Republic in the taiga zone), the abandonment of arable land after 1991 likely plays a significant role. Likewise, a decline in the frequency of extreme rainfall events (> 50 mm) may have played a role. All of these factors contribute to a reduction of surface runoff to the gullies and their subsequent stabilization. © 2018 John Wiley & Sons, Ltd.status: publishe

Trend Analysis of Total Column Ozone over New Delhi, India

Total Column Ozone measurements from Total Ozone Mapping Spectrometer (TOMS) onboard satellite Nimbus 7, Meteor 3 and Earth Probe have been used to determine trends in column ozone over New Delhi. Long term trend obtained with ozone time series data and least square fitting without removing Seasonal cycle, QBO, Solar effect and ENSO, shows that ozone concentration is decreasing by 2.11 (+/- 1.04) % per decade over New Delhi. Therefore, to calculate the exact trend, multifunctional regression model have been used to remove the effect ofseasonal cycle, solar cycle, QBO and ENSO. The obtained long term trend with multifunctional regression model shows that column ozone over Delhi is actually decreasing by 1.83 (+/- 1.02) % per decade. The trend obtained from ozone time series data with least square fit overestimates multifunctional regression model by about 15%. The objective of this paper is to present the result of a long term trend analysis of the TOMS total ozone data over New Delh

Diagnostische Verifikation des Atmosphärischen Wasserkreislaufs Vorhergesagt mit Regionalen Mesoskaligen Modellen und Ensemblesystemen

Precipitation is the final component of a complex process chain of the atmospheric water cycle. All model errors in this process chain are consequently accumulated in quantitative precipitation forecasts (QPF). To diagnose the shortcomings of QPF, the following four key variables of the atmospheric water cycle have been evaluated: integrated water vapour content (IWV), low cloud cover (LCC), high cloud cover (HCC), and precipitation rate at the surface. This comprehensive verification of all key variables is performed for nine deterministic models and four ensemble systems from the forecast demonstration experiment of Mesoscale Alpine Program (MAP D-PHASE) using measurements from the General Observation Period (GOP) over Southern Germany for summer 2007. Verification of individual key variables reveals that most of the models forecast the mean values of IWV very well; however, they show large biases in the mean values of LCC, HCC, and precipitation. At certain times and locations, all models show large errors in all key variables, especially in HCC and precipitation. The models with convection parameterization predict diurnal precipitation maxima a few hours earlier than observations, whereas deep-convection-resolving models forecast the diurnal maxima too late. Early initiation of convection is a specific problem of the Tiedtke convection scheme. The forecast performance of high resolution models is superior to their corresponding low resolution models for all key variables, except for IWV. Multivariate verification fails to quantify the shortcomings in QPF, perhaps due to the limited availability of observations. Multimodel multiboundary ensemble prediction systems (EPS) show superiority in the prediction of all key variables and also has better representation of forecast uncertainty compared to EPS based on a single model. EPS which accounts the small-scale perturbations, due to the uncertainty in boundary and initial conditions from limited area models, lead to better forecasts for strong events. However, all the EPS evaluated in this study are underdispersive which clearly implies that they are not able to account for all possible uncertainties of short-range forecasts