*3.2. Trend Analysis*

#### 3.2.1. Precipitation

No significant trends are detected in historical annual and wet season precipitation for any study regions. Similar findings have also been reported in relevant previous studies [14]. During the projection period (2020–2099), a limited amount (no more than 15%) of model projections show significant trends (Table 5). For annual precipitation, only one projection (out of 20) has statistically significant trend for Sacramento River, South Coast, and Tulare Lake regions; three projections indicate significant trends in Central Coast and North Lahontan regions; for other regions, only two projections show significant trends. The slopes of those significant trends are all positive.


**Table 5.** Trend information of projected precipitation.

<sup>1</sup> Significance level 0.05.

For wet season precipitation, no projections show any significant trends for the driest two regions (Colorado River and South Lahontan). For San Francisco Bay, Central Coast, South Coast, San Joaquin River, Tulare Lake, and North Lahontan regions, the projections showing significant trends are exactly the same as those showing significant trends in annual precipitation. For the two wettest regions (North Coast and Sacramento River), three projections show significant changes. Different from

annual precipitation, two projections on wet season precipitation (one for Central Coast region and the other for Sacramento River region) exhibit a decreasing tendency. Nevertheless, similar to the annual precipitation, no significant changes are expected in the majority of climate model projections on wet season precipitation through 2099.
