Answer:
1.- Semiarid
2.- soil, humid
3.- Evaporation, 
4.- Steppe
Step-by-step explanation:
(1) Steppe is a semiarid ecosystem, with few vegetation and water.
 (2) In deserts, humidity is close to 0%, that is the reason why there is no vegetation, and the soil is thin, because does not need to sustain a plant. 
 (3) In deserts for example, the evaporation rate is too high because of the lack of vegetation that can retain humidity in its body. 
 (4) A desert has a drier climate than a Steppe because of the lack of vegetation and a soil that is not going to fix water in it. 
Hope this info is useful