## 3 Results and Discussion
### Temperature Trends
Most of the water from these rivers comes from snowmelt, and the increase in temperature trends in the winter season (DJF) would mean acceleration in the snow melting season. These results agree with other research conducted in other mountain systems [71]. In those three months, high positive trends (+0.02-0.03 \({}^{\circ}\)C year\({}^{-1}\)) have been found all over California, in nearly 90% of the stations (Figure 2). That rapid melt can cause difficulties in the maintenance of fresh water in agriculture and for human consumption, as suggested by some researchers [47; 72; 73; 74]. The Central Valley can be more vulnerable to warming-driven drought if reductions in water supply cause reductions in irrigation [75]. The map for February (Figure 3) revealed a lack of clear trends due to the fact that there is no distinct direction in positive or negative temperature trends. These findings support the results shown on the NOAA website ([[https://www.ncdc.noaa.gov/temp-and-precip/us-trends/](https://www.ncdc.noaa.gov/temp-and-precip/us-trends/)]([https://www.ncdc.noaa.gov/temp-and-precip/us-trends/](https://www.ncdc.noaa.gov/temp-and-precip/us-trends/)) accessed 10 February 2021), which points out that \"strong trends are not shown, this is because the period studied is defined by warm Februurys in the 90's and cold ones in 00's in California State\". We can see (Figure 3) great similarities in both March and April temperature trends. During these months, the northeast of California tends to show slightly negative temperature trends in 30% of the stations (\(-\)0.01 \({}^{\circ}\)C year\({}^{-1}\)), while in South Sierra Nevada, the Mojave Desert, Los Angeles, Imperial Valley, San Gabriel and San Bernardino Mountain, the average temperature had gone up +0.04 \({}^{\circ}\)C year\({}^{-1}\). The results in May for California are different from the rest of the year because, in the southern coastal region and San Francisco Bay, a negative trend appeared (\(-\)0.01 \({}^{\circ}\)C year\({}^{-1}\)). This could be related to the penetration of coastal marine fog, which varies seasonally [76]. That is important due to the moisture content of air near the surface, making this a regional phenomenon with strong local patterns [77]. This cooling effect that we have mentioned before has been explained by previous investigation [78], although in this research it seems to have a lesser  
Figure 2: Percentages of meteorological stations with positive and negative trends. effect--instead of being negative, trends are close to zero, similar to what has been mentioned in other research. In fact, coastal fog along the California coast, critical to San Francisco Bay Area climate, is less frequent than before [79]. During June, July and August, the temperature has risen all over the State (+0.065 \({}^{\circ}\)C year\({}^{-1}\)), showing more territories with statistically significant trends in July and August (30% of the stations analysed). Figure 3 shows highly significant trends in these months in the northern part of the State, Mt. Shasta, part of the Cascade Ranges and Lake Tahoe, and a huge area of Death Valley and the Mojave Desert. These results are related to those which confirm increases in trends of heat waves in south California [80], becoming more and more frequent in urban environments than in more rural surroundings. As a result of this is a higher risk of heat-related births [81] and deaths as well as an increase in wildfires. Increases of +0.05 \({}^{\circ}\)C year\({}^{-1}\) in Sacramento and San Joaquin Valley are in this research comparable to June and August. The trends in September show great similarities to July and August but with less statistically significant areas. Nevertheless, in October, there was a negative trend (\(-0.01\)\({}^{\circ}\)C year\({}^{-1}\)) without statistical significance in the north, particularly in coastal areas, covering Eureka city up to Shelter Cove, as had been stated by previous research [18].