The relief is flat but the meso- and microtopography undulates, with rises, slopes and depressions, causing poor drainage of surface and subsurface water. In addition, because the upper reaches of the Huang and Hai river systems flow through loess, their waters have a very high silt content which settles in the gentler plains channels. The consequent elevation of the river beds above the surrounding land surface has intensified lateral seepage and caused the water table to rise. Climatically, the region is semi-humid, but because of the Pacific monsoon, annual precipitation is unevenly distributed. Summer is blazing hot and rainy, with rainfall concentrated in July and August storms.
Spring is windy with little rain, so evaporation is very intense.
Quite often, insufficient moisture is available for spring sowing, and sometimes throughout the entire wheat-growing period. The resulting intense accumulation of salts in the soil presents some difficulties to spring sowing and the normal growth of summer-harvested crops. It is very difficult under these circumstances to gain high yields without irrigation. Yields of fall crops are low and unstable, with no harvest at all guaranteed in the depressions. The light and heat conditions of this region are suitable for two crops a year or three crops in two years.