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The moist periods with high precipitation and periods of atmospheric droughts are a potential great hazard to the functioning of ecosystems and different sectors of the national economy in the Lublin region. Therefore, a recognition of time variability of these atmospheric phenomena and the conditions of their occurrence are the main aims of this paper.

The analysis of the precipitation‐free periods was based on the meteorological data from the years 1951‐2009 recorded in the Meteorological Observatory of the Maria Curie‐Skłodowska University in Lublin. Main hydrological data concerning dynamics of groundwater table and surface water table came from the measurement network of the Institute of Meteorology and Water Management.

Very long precipitation‐free periods, lasting over 20 days, appeared only seven times – once a year in 1953, 1956, 1959, 1971, 1983, and twice in 2000. Since the 1980s, the number of precipitation‐free periods has been decreasing parallel to the higher frequency of downpours and increasing annual precipitation totals. In the years 1981‐1994, the following phenomena were observed in the Lublin region: decrease of river mean discharges, groundwater‐table lowering, lowering of lake surfaces, disappearance of springs, and the shortening of the upper reaches of rivers. However, replenishment of water resources and more frequent meteorological extreme events have been recorded in the Lublin region since the second half of the 1990s. Therefore, local flood and inundations have occurred, and flood hazard in larger river valleys has increased.

Examination of time variability of these atmospheric phenomena and conditions of their occurrence should contribute to the development of effective ways and techniques of management of water resources in the regional economy in order to reduce economic losses.

In many parts of the globe, drought is becoming frequent and severe. Drought is related to water and for that reason, this chapter begins by describing the movement of water on planet earth. In a second phase, the drought concept is defined and the different types of drought are identified. At the end, the impacts and the relationship between climate change and drought are described.

The Monsoon Asian region has a much wider rainfall distribution than other regions of the world. The countries in this region are characterized mostly by floods and typhoons, which result from the interplay among the ocean, the atmosphere, and the land. Thus, many factors affect the strength of the rainfall, including sea surface temperatures in the Indian and Pacific Oceans, variations in solar output, land snow cover and soil moisture over the Asian continent, and the position and strength of prevailing winds. The links between these factors and monsoons appear to wax and wane over time, and the observational record is too short to explain this longer-term variability. Precipitation and surface wind maps of Asia during the summer months of June to August show the average spatial patterns of monsoon circulation and moisture.

Case studies from many countries indicate that even when rainfall is high drought can still occur. Droughts have been recorded in Bangladesh, where the rainfall is 2,300mm per year, and in Luang Prabang, Laos, where the annual rainfall is 3,200mm. Similarly, the highest Standardized Precipitation Index (SPI) value of 2.78 indicates a possibility of floods in Cambodia. Identification of a threshold SPI value is necessary to pinpoint impending drought. Since SPI values reflect only the rainfall situation and not the existing water availability in reservoirs and canal systems, such a detailed impact-assessment study should also compare the duration of a negative SPI value with that of reduction in the available water from various sources, including groundwater, reservoirs, and canal irrigation systems. So drought occurs not only because of lack of rainfall but also because of bad practices of water usage and water management.

Year‐to‐year fluctuations of rainfall in the northern Negev desert provide an opportunity to characterize and assess the temporal dynamics of desertification, phenology, and drought processes. Such information was retrieved and analyzed by combined use of satellite imageries in the reflectivity and thermal spectral bands. Data covering four years of coarse spatial resolution and images from a high revisit time satellite, namely the NOAA‐14, were used. The images were processed to produce the normalized difference vegetation index (NDVI) and the land surface temperature (LST). These measures were applied to the sand field in the northwestern Negev (Israel), which is almost totally covered by biological soil crusts, and to an adjacent region in Sinai (Egypt), consisting mainly of bare dune sands. Various manipulations of the data were applied. Time series presentation of the NDVI and LST reveals that the NDVI values correspond to the reaction of the vegetation to rainfall and that LST values represent seasonal climatic fluctuation. Scatterplot analysis of LST vs NDVI demonstrates the following: the two different biomes (Sinai and the Negev) exhibit different yearly variation of the phenological patterns (two seasons in Sinai moving along the LST axis, and three seasons in the Negev, where the NDVI axis represents the growing season); the Sinai has an ecosystem similar to that found in the Sahara, while the Negev, only a few kilometers away, has an ecosystem similar to the one found in the Sahel; and drought indicators were derived by using several geometrical expressions based on the two extreme points of the LST‐NDVI scatterplot. The later analysis led to a discrimination function that aims to distinguish between the drought years and the wet years in both biomes. Results from the current study show that a great deal of information on dryland ecosystems can be derived from four, out of five, NOAA/AVHRR spectral bands. The NDVI is derived from the red and the near‐infrared bands and the LST from the two thermal bands. Combined use of these two products provides more information than any product alone.

This paper seeks to address the issue of persistent and widespread drought conditions during 2000 and 2001, which were the apparent cause of the decline of water levels in the reservoirs of Brazilian hydroelectric power plants.

This issue is addressed here through a case study of the hydroclimatology of the Paraíba river basin, in Southeast Brazil, home to four large multi‐purpose operational reservoirs.

The data analysis shows that neither changes in the frequency nor magnitude of extreme hydrological events (droughts and floods) nor in annual rainfall amounts can be detected from the existing climate record. The explanation is consistent with the fact that the terrestrial water and energy cycles are tightly, and non‐linearly, coupled through evapotranspiration.

Therefore small change in the seasonality of rainfall can have a significant impact on the basin's overall hydrologic regime, and thus on the availability of water resources.

Often, adaptation and resilience to climate variability are discussed in the context of catastrophic events such as floods and droughts. This study suggests that a different type of impacts, those associated with subtle, yet persistent changes of seasonality in the terrestrial water cycle, cannot be ignored in studies of long‐term sustainability of water resources.

Bangladesh has a long history of dealing with seasonal changes resulting in droughts and floods. Three major rivers, the Ganges, Brahmaputra and Meghna (GBM) come to a confluence, forming the GBM floodplain. There is a specific time window (June to September) when most of the runoff occurs and over 90% of their combined flow is discharged into the Bay of Bengal. As a result, the seasonal monsoons result in wet and dry seasons, making Bangladesh vulnerable to both floods and droughts. Climate change will likely alter characteristics such as timing and intensity, therefore increasing the challenge of adaptation. Socioeconomic conditions and high-population density limit the country's ability to adapt to these hydro-meteorological extremes. Although climatic variability causes severe damage and loss of life in Bangladesh, examples of local adaptation to the annual rhythm of seasonal variation can be found in flood-prone areas. Scientific modeling has resulted in more robust and efficient early warning systems that have greatly decreased the loss of life from climate hazards in recent years. However, positive impacts from models are limited by complex social concerns that are pervasive across the country.

The purpose of this paper is to assess the extent of climate change likely to be manifested in the MENA region using statistical tools as well as outputs from physics‐based General Circulation Models (GCMs).

Atmospheric temperature and precipitation primarily capture climate change features and are considered the drivers of other manifestations of climate change such as rises in sea‐level, tropical cyclone intensities, severe floods, prolonged droughts, and retreating ice. Data on atmospheric temperature and precipitation have been statistically analysed for trend, distribution and variability in this study. Long‐range prediction is then made using time series analysis. Long‐range projections have also been made by many investigators using physics‐based GCMs and the Fourth Assessment Report of IPCC provides a summary. IPCC projections are not indisputable because of some inherent limitations of GCMs. A comparative study is made between statistical predictions and IPCC projections, as well as forecasts from some GCMs specifically applied to the region, to develop a more reliable forecast scenario. Water resources projects are quite vulnerable to changes in atmospheric temperature and precipitation amounts. The various aspects of planning, design and management of water resources projects which are likely to be influenced by climate change are discussed.

There is considerable variability in atmospheric temperature and precipitation in recent observations but if the variability is filtered out and the underlying trend extrapolated it is found that there is in general an agreement between IPCC projections and statistical predictions. For rise in atmospheric temperature projections made from many GCMs applied to the region, as well as projections summarised in the Fourth Assessment Report of IPCC, appear to be good estimates to be included in design considerations. For precipitation, statistical predictions are perhaps a better choice because GCM projections are less reliable with precipitation since associated meteorological processes occur at a much smaller scale than the grid size of a GCM. For low‐lying coastal regions sea‐level rise and more frequent extreme climatic events such as tropical cyclones add to the dimensionality of design considerations especially for infrastructure design.

This paper presents a comparative study of possible climate change in the long‐term between physics‐based model projections and statistical predictions. This should provide greater insight into climate change that is expected in MENA and reduce uncertainty, thereby instilling greater confidence in water resources planners and practitioners to incorporate climate change aspects into decision making. This research is believed to be particularly helpful because of scant research work done on this part of the globe on climate change.

It is now established by the global scientific community that climate change is a hard reality but the changes are complex in nature and to a great extent uncertain. Global circulation models (GCMs) have made significant contributions to the theoretical understanding of potential climate impacts, but their shortcomings in terms of assessing climate impacts soon became apparent. GCMs demonstrate significant skill at the continental and hemispheric scales and incorporate a large proportion of the complexity of the global system. However, they are inherently unable to represent local subgrid-scale features and dynamics. The first generation approaches of climate change impact and vulnerability assessments are derived from GCMs downscaled to produce scenarios at regional and local scales, but since the downscaled models inherit the biases of their parent GCM, they produce a simplified version of local climate. Furthermore, their output is limited to changes in mean temperature, rainfall, and sea level. For this reason, hydrological modeling with GCM output is useful for assessing impacts. The hydrological response due to change in climate variables in the Amu Darya River Basin was investigated using the Soil and Water Assessment Tool (SWAT). The modeling results show that there is an increase in precipitation, maximum and minimum temperature, potential evapotranspiration, surface runoff, percolation, and water yields. The above methodology can be practiced in this region for conducting adaptation and mitigation assessments. This initial assessment will facilitate future simulation modeling applications using SWAT for the Amu Darya River Basin by including variables of local changes (e.g., population growth, deforestation) that directly affect the hydrology of the region.