Medieval Islamic Environment
We can divide the environmental history of medieval West Asia (during the time of the Islamic Empire) into three different phases. In the early phase, from the 600s to about 800 AD, in the time of the Umayyad and the Abbasid Caliphs, the climate was probably pretty similar to what it had been for a thousand years before that. You can get a good idea of what that was like by checking out the earlier environment of West Asia and North Africa. Basically, the weather was dry and hot, and there was always a shortage of water.
But by the Middle Ages, people in West Asia were pretty good at changing their environment to make it more useful to them. They dug canals leading away from all the major rivers - the Nile, the Tigris, the Euphrates - to irrigate their fields. Even in Iran, where there aren't any really big rivers, people dug many irrigation canals like the Haffar, reservoirs, aqueducts, and cisterns so they could make the best use of their water. Under the Islamic caliphs, with good irrigation systems, West Asia grew plenty of food and people thought of it as one big garden.
In the second phase, the Medieval Warm Period between about 800-1200 AD probably affected West Asia just as it affected people in Europe, in Central America, and in North America. Nobody knows much about it yet, but probably West Asia and North Africa became even warmer and drier than they had been before. Possibly the climate change encouraged West Asian farmers to grow Indian crops like cotton, sugar, and oranges that they had not grown before.
The third phase of the environmental history of the Islamic Empire is a colder period known as the Little Ice Age. The Little Ice Age that started about 1200-1300 AD may have encouraged the Mongols to leave the cold of Siberia to invade warmer West Asia and China.
But no matter how careful you were with water, or how much the climate changed, on the whole the entire Islamic Empire was still a fairly hot and dry place, and there was always a shortage of water wherever you went.