Early blight caused by Alternaria solani (Ell. and Mart.) is one of the most important economic diseases, which caused considerable loss in their yield and quality under Egyptian conditions. Aim the research was to study the relationship between climate change and disease severity for prediction in future seasons. Disease severity was recorded for three growing periods i.e. summer (May. to Aug), autumn (Jul. to Oct) and winter (Nov. to Mar.), at three governorates (Behira, Ismailia, and Assuit) during growing seasons 2016/2017-2017/2018. Severity of early blight disease on tomato has been predicted by regression estimated accumulative disease severity values during 2007/2008 to 2015/2016 season and average max and min temperature and humidity through these seasons. Prediction of disease has been formed as Y= b0+b1x1+b2x2+.......... bqxq. Three models were created to describe the severity disease by multiple regressions (MINITAB® program). The highest value of early blight disease was recorded through season 2017/2018, while the lowest value was recorded during season 2016/2017. Also, highly disease severity was estimated during summer period compared with autumn and winter growing periods, but through winter growing period was the least severity and moderately severity estimated in the autumn growing period. Influence of environmental conditions on the severity of early blight disease during seasons from 2007/2008 to 2015/2016, in Behira governorate, the highest disease severity was showed in season 2010-2011, and the lowest disease was in season 2012-2013, but in Ismailia governorate, highest disease severity was estimated in season 2010-2011and lowest disease was recorded in season 2013-2014 and in Assuit governorate, the highest value of disease was in season 2010-2011, and the lowest value was in season 2013-2014. For Forecasting, significantly differences noticed between disease severity through 2020/2030, 2030/2040 and 2040/ 2050s seasons compared with 2008/2018s seasons and thier relation with climate change in tested governorates, where severity of tomato early blight disease was icreased from 11.8% during 2008/2018s seasons to 2040/ 2050s seasons 15.4% during at Behira governorate, from 18.8% during 2008/2018s seasons to 2040/ 2050s seasons 36.3% during at Ismailia governorate and from 18.8% during 2008/2018s seasons to 2040/ 2050s seasons 40.4% during at Assuit governorate with slight change in maximum or minimum temperatures and percentage of relative humidity.