The analysis of the current state of weather and climatic conditions and evaluation of their predicted changes for immediate and distant prospect in the drained areas of Ukrainian Polissia region was carried out in the article. The main trends in changes of meteorological characteristics and their possible effect on the conditions of functioning water management and ameliorative objects and complexes as well as on the natural and ameliorative state of drained areas were identified. The research uses a method of predictive-simulation modelling with used predictive assessment models of normalized distribution of the basic meteorological characteristics in the long-term and one-year vegetation context. According to the results of the research it was established that, for today a high variability in meteorological characteristics can lead to the significant deterioration of operation conditions of water management and ameliorative objects and units, as well as natural and ameliorative conditions of drained lands in Polissia region as a whole. Core measures regarding the adaptive potential enhancement and development in the region under the conditions of climate change were examined.

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Ecological-reclamation state of rice irrigation systems harvest of cultivated crops determined by a number of factors, including natural (soil, topographical, hydrogeological, climatic factors) and technological (irrigation norm, designs and parameters of irrigation and drainage networks, etc.) factors. One of the main factors influencing the formation of rice yield which is traditionally grown by flooding technology is the efficiency of the rice irrigation system’s design. Construction features of irrigation fields and their parameters (distances between the drains, depth of the drainage network) affect the intensity of the processes of salinization of soils and groundwater. Analysis of the components of salt balances of rice fields with different parameters and designs on example of the Danube rice irrigation systems showed that fields with the distances between the drains from 200 to 250 m have significant advantages over Krasnodar-type fields with the same parameters and over fields with 500 m distance between the drains creating optimal salt regime for rice and, accordingly, obtaining higher yields of rice. As on the card-checks with drainage with the distances between the drains 500 m uniform desalinization of soils on all area cannot be reached and yield of rice on them is close to 20 c/ha such card-checks with drainage must be converted into card-checks with drainage with the distances between the drains 250 m.

In modern conditions, there are cardinal climate changes on the Earth as at the planetary scale, as at the regional level. According to numerous hydrometeorological characteristics and indicators, climatologists specialists concluded that Ukraine also take place significant climatic changes in the last 10–25 years. In complicated natural-technical systems, which include irrigation and drainage systems (IDS) on drained lands, the selection of regime-technological and technical solutions on different levels of the decision including the time, should be based on the appropriate meteorological information for selecting climatologically optimal management strategies for such systems in the long-term and annual periods. The decisive influence on the formation of water and the overall natural reclamation modes of reclaimed land and harvest crops in many cases depends exactly from climate or weather conditions. Thus, it is necessary to have available data about their implementation to the relevant object as for number of previous years retrospective observations and the forecast period of functioning of the object. Therefore, forecasting of weather and climate conditions become an indispensable condition for implementation of assessing the overall effectiveness of IDS operation. To solve this problem we performed large-scale computer experiment for multi-year retrospective and current data observations in the area of Zhytomyr Polissya. Were planned and implemented the following variants of studies – «Base», «Transitional», «Recent», «CCCM», «UKMO». The forecast was done for five years of typical groups of vegetation periods regarding conditions of heat and moisture provision (very wet – 10%, wet – 30%, average – 50%, dry – 70%, very dry – 90%) on such basic meteorological characteristics: air temperature; precipitation; relative air humidity; defi cit of air humidity; photosynthetically active radiation (PAR); coeffi cient of moisture provision (the ratio of precipitation to evapotranspiration). Obtained results of comparative assess-ment of climatic conditions in Zhytomyr Polissya zone, suggests that for most of the basic meteorological parameters, already there are changes that in the short term may exceed 10% of the critical ecological threshold, which will lead to relevant irreversible changes in the state of the environment in the region.

This chapter considered qualitatively different approaches to the water regime model of drained lands implementation. The fundamental difference of these approaches is that the regime forecast calculations on a long-term basis are performed for schematized natural reclamation conditions by typing meteorological regimes in the calculation periods of vegetation, appropriate schematization, and parameterization of water regulation of drained lands. Secondly, it is proposed in the framework of the balance equation to perform based on certain patterns, to calculate the process of water regime based on the relationship and interdependence of its elements at the boundaries and in connection with the process of redistribution of moisture within the active layer of soil in relation to its moisture content and storage capacity. Considered methods and models of water regime allow determining both potentially possible due to meteorological and agrotechnical conditions and effective values of irrigation norms in the development of design modes of irrigation by irrigation and subsoil at drained lands.