(1) Natural causes: global warming, shrinking glaciers in Qilian Mountains, and reduced melting water of snow and ice.

Man-made reasons: With the continuous growth of population and the rapid development of industrial and agricultural production, the water consumption in the basin has increased rapidly.

(2) Lakes are shrinking and drying up, natural vegetation withers and dies, and the process of land desertification and salinization is accelerating; (Overexploitation of groundwater) The groundwater level drops and the salt content increases.

(3) Reduce the planting area of crops with high water consumption, implement the project of returning farmland to grassland, implement advanced technologies such as drip irrigation and infiltration irrigation on a large scale, and vigorously develop water-saving and efficient agriculture.

Test analysis:

Problem (1), the reduction of river water quantity should be considered from two aspects: natural and man-made reasons; Natural causes are related to climate warming, and human causes are related to the increase of water consumption in the basin.

Problem (2), due to the over-utilization of rivers, rivers are cut off, lakes are dried up, and the number of natural vegetation is reduced; Downstream areas turn to a large number of groundwater exploitation, which will lead to the decline of groundwater level, the increase of salt content and the aggravation of salinization.

Question (3), as can be seen from the figure, in Shiyang River Basin, farmland irrigation is the most important way of water use. To solve the problem of water resources in this basin, it is necessary to reduce the irrigation water consumption of farmland and improve the efficiency of agricultural water use.

Comments: This topic is less difficult, involving the causes of water reduction in Shiyang River Basin, the ecological environment problems caused by water reduction and the ways to solve the water resources problems in Shiyang River Basin. This topic also fully examines students' flexible application ability and language organization ability.