SFEWS provides credible scientific information on California's complex water issues, linking new science to policy with great effect. SFEWS retains a regional focus on the San Francisco Bay and the Sacramento–San Joaquin Delta, also known as the Bay–Delta watershed. At the heart of open access from the California Digital Library, SFEWS's scholarly output ranks #1 for the UC Davis Institute of the Environment and ranks #3 campus wide.
Volume 16, Issue 4, 2018
Hourly Analyses of the Large Storms and Atmospheric Rivers that Provide Most of California’s Precipitation in Only 10 to 100 Hours per Year
California is regularly affected by floods and droughts, primarily as a result of too many or too few atmospheric rivers (ARs). This study analyzes a 2-decade-long hourly precipitation data set from 176 California weather stations and a 3-hourly AR chronology to report variations in rainfall events across California and their association with ARs. On average, 10–40 and 60–120 hours of rainfall in southern and northern California, respectively, are responsible for more than half of annual rainfall accumulations. Approximately 10% to 30% of annual precipitation at locations across the state is from only one large storm. On average, northern California receives 25 to 45 rainfall events annually (40% to 50% of which are AR-related). These events typically last longer and have higher event-precipitation totals than those in southern California. Northern California also receives more AR landfalls with longer durations and stronger Integrated Vapor Transport (IVT). On average, ARs contribute 79%, 76%, and 68% of extreme-rainfall accumulations (i.e., top 5% events annually) in the north coast, northern Sierra, and Transverse Ranges of southern California, respectively.
The San Francisco Bay Area terrain gap in the California Coast Range allows more AR water vapor to reach inland over the Delta and Sacramento Valley, and thus influences precipitation in the Delta’s catchment. This is particularly important for extreme precipitation in the northern Sierra Nevada, including river basins above Oroville Dam and Shasta Dam.
This study highlights differences between rainfall and AR characteristics in coastal versus inland northern California — differences that largely determine the regional geography of flood risks and water reliability. These analyses support water resource, flood, levee, wetland, and ecosystem management within the catchment of the San Francisco Estuary system by describing regional characteristics of ARs and their influence on rainfall on an hourly time-scale.
- 1 supplemental PDF
Resource managers rely on long-term monitoring surveys conducted in the San Francisco Estuary to evaluate the status and trends of resident fish populations in this important region. These surveys are potentially confounded because of the incomplete detection of individuals and species, the magnitude of which is often related to the same factors that affect fish populations. We used multistate occupancy estimators to evaluate the distribution, abundance, and detection probability of four fish species collected during 1995–2015 with three long-term surveys. Detection probabilities varied positively with fish abundance and negatively with Secchi depth. Detection varied among species and was greatest for the 20-mm Survey and least for the midwater trawl used for the midwater trawl used in the San Francisco Bay Study. Incomplete detection resulted in underestimates of occupancy and abundance across species and surveys and were greatest for the Bay Study. However, trends in occupancy and abundance of the study period appeared to be unbiased. Fish occupancy and abundance were generally related to salinity or specific conductance, day-of-the year, and water temperature, but the nature of the relations varied among surveys and species. There also was strong spatial and temporal dependence in species-specific occupancy and abundance that changed through time and were unrelated to the covariates considered. Our results suggest that managers consider incorporating methods for estimating detection and adjusting data to ensure data quality. Additionally, the strong spatio-temporal patterns in the monitoring data suggest that existing protocols may need to be modified to ensure that data and inferences reflect system-wide changes rather than changes at a specific set of non-randomly selected locations.
- 2 supplemental PDFs
Non-Native Fish Predator Density and Molecular-Based Diet Estimates Suggest Differing Impacts of Predator Species on Juvenile Salmon in the San Joaquin River, California
The Sacramento-San Joaquin Delta is a major survival bottleneck for imperiled California salmonid populations, which is partially due to a multitude of non-native fish predators that have proliferated there throughout the 20th century. Understanding the diets of salmonid predators is critical to understanding their individual impacts, role in the food web, and the implications for potential management actions. We collected the stomach contents of Striped Bass Morone saxatilis, Largemouth Bass Micropterus salmoides, Channel Catfish Ictalurus punctatus and White Catfish Ameiurus catus sampled from three 1-km reaches in the lower San Joaquin River in 2014 and 2015 during the peak juvenile salmon outmigration period. We tested each stomach (n = 582) for the presence of juvenile Chinook Salmon Oncorhynchus tshawytscha and other prey items using a genetic barcoding technique. Channel Catfish had significantly higher frequency of Chinook Salmon in their stomachs (27.8% of tested Channel Catfish contained Chinook Salmon DNA), compared to the other three predators (2.8% to 4.8%). However, non-native fish species occurred at greater frequencies in the diets of all four predator species than salmon. Using depletion estimation from electrofishing, we were able to generate population densities for Striped Bass and Largemouth Bass in our reaches. Largemouth Bass were evenly distributed throughout all three reaches, at a mean density of approximately 333 (± 195 SE) per km of river. Striped Bass were patchily distributed, ranging from 21 to 1,227 per km. Extrapolating the frequency of salmon detected in stomachs to the predator abundance estimates, we estimate that the population of Largemouth Bass we sampled consumed between 3 and 5 Chinook Salmon per day per 1-km study reach (consumption rate of 0.011 salmon per predator per day), whereas the Striped Bass population consumed between 0 and 24 Chinook Salmon per day (0.019 salmon per predator per day).
Alternative Juvenile Production Estimate (JPE) Forecast Approaches for Sacramento River Winter-Run Chinook Salmon
Sacramento River winter-run Chinook salmon are listed under the Endangered Species Act as Endangered and there are substantial efforts to estimate, predict, and limit mortalities at various stages of their life cycle. One such effort is the annual forecast of the number of juvenile winter-run entering the Sacramento-San Joaquin Delta. The natural-origin Juvenile Production Estimate (JPE) is defined as the number of winter-run juveniles produced from natural spawning areas that enter the Delta, and its forecast is used to determine the allowable level of winter-run incidental take at the state and federal pumping facilities located in the south Delta. Current monitoring programs in the Sacramento Basin do not allow for direct estimation of the JPE and thus various methods have been used to forecast this value annually. Here we describe three alternative methods for forecasting the natural-origin JPE. The methods range from the status quo approach (Method 1), which expresses the JPE forecast only as a point estimate, to two other methods that account for forecast uncertainty to various degrees. A comparison of JPE forecasts for 2018 across the three methods indicates that relative to Method 1, Methods 2 and 3 result in lower JPE forecasts, by 24 and 18 percent, respectively, primarily owing to lower forecasts of the fry-to-smolt transition and the smolt survival rate occurring downstream of Red Bluff Diversion Dam. Because post-hoc estimates of juvenile winter-run abundance at the entrance to the Delta do not currently exist, we are unable to evaluate forecast skill among the three methods.
- 1 supplemental PDF
SFEWS hutoa habari ya kisayansi ya kuaminika juu ya masuala tata ya maji ya California, ikiunganisha sayansi mpya na sera na athari kubwa. SFEWS inaendelea kuzingatia kikanda juu ya San Francisco Bay na Sacramento-San Joaquin Delta, pia inajulikana kama Bay-Delta watershed. Katika moyo wa upatikanaji wazi kutoka Maktaba ya Dijiti ya California, matokeo ya kisayansi ya SFEWS ni nafasi ya kwanza kwa Taasisi ya Mazingira ya UC Davis na nafasi ya tatu katika chuo kikuu. "Kama ilivyoelezwa katika makala ya ""Mvua ya California"" ya mwaka 2018, ""Mvua ya California"" ni moja ya sababu za mvua ya California ya kawaida, na ni moja ya sababu za mvua ya California ya kawaida." Utafiti huu unachambua seti ya data ya mvua ya kila saa ya miongo miwili kutoka vituo vya hali ya hewa vya 176 vya California na kronolojia ya AR ya masaa matatu ili kuripoti tofauti katika matukio ya mvua kote California na ushirika wao na ARs. Kwa wastani, masaa 10 hadi 40 ya mvua katika kusini na kaskazini mwa California ni zaidi ya nusu ya mkusanyiko wa mvua ya kila mwaka. Karibu asilimia 30 ya mvua ya kila mwaka katika maeneo ya jimbo hilo hutokana na dhoruba moja tu kubwa. Kwa wastani, kaskazini mwa California hupokea matukio ya mvua 25 hadi 45 kila mwaka (40% hadi 50% ambayo inahusiana na AR). Matukio haya kwa kawaida hudumu kwa muda mrefu na yana jumla ya matukio ya mvua ya juu kuliko wale katika kusini mwa California. Kaskazini mwa California pia hupokea maporomoko zaidi ya AR na muda mrefu na Usafiri wa mvuke uliounganishwa (IVT) wenye nguvu. Kwa wastani, ARs huchangia 79%, 76% na 68% ya mkusanyiko wa mvua kali (yaani, matukio ya juu ya 5% kila mwaka) katika pwani ya kaskazini, Sierra ya kaskazini, na Transverse Ranges ya kusini mwa California. San Francisco Bay Area eneo pengo katika California Coast Range inaruhusu zaidi AR mvuke wa maji kufikia ndani ya nchi juu ya Delta na Sacramento Valley, na hivyo ushawishi mvua katika Delta ya catchment. Hii ni muhimu hasa kwa mvua kali katika kaskazini mwa Sierra Nevada, ikiwa ni pamoja na mabwawa ya mto juu ya Bwawa la Oroville na Bwawa la Shasta. Utafiti huu unaonyesha tofauti kati ya mvua na sifa za AR katika pwani dhidi ya ndani ya California ya Kaskazini - tofauti ambazo huamua sana jiografia ya kikanda ya hatari za mafuriko na kuegemea maji. Uchambuzi huu unasaidia usimamizi wa rasilimali za maji, mafuriko, mabwawa, maeneo ya mvua, na mifumo ya ikolojia ndani ya eneo la maji la San Francisco Estuary, kwa kuelezea sifa za kikanda za AR na ushawishi wao juu ya mvua kwa kiwango cha saa. "Mafunzo ya ""Usimamizi wa Rasilimali"" hutegemea uchunguzi wa muda mrefu uliofanywa katika San Francisco Estuary ili kutathmini hali na mwelekeo wa idadi ya samaki wa makazi katika mkoa huu muhimu." Uchunguzi huu unaweza kuwa na usumbufu kwa sababu ya kugundua watu na spishi zisizo kamili, ukubwa ambao mara nyingi unahusiana na sababu zile zile zinazowathirika idadi ya samaki. Kwa mfano, tulitumia takwimu za idadi ya watu katika majimbo kadhaa ili kutathmini usambazaji, wingi, na uwezekano wa kugundua spishi nne za samaki zilizokusanywa wakati wa 1995-2015 na uchunguzi wa muda mrefu. Uwezekano wa kugundua ulitofautiana kwa manufaa na wingi wa samaki na kwa hasara na kina cha Secchi. Ugunduzi ulitofautiana kati ya spishi na ulikuwa mkubwa kwa uchunguzi wa 20mm na mdogo kwa trawl ya katikati ya maji iliyotumiwa kwa trawl ya katikati ya maji iliyotumiwa katika Utafiti wa San Francisco Bay. Ugunduzi usio kamili ulisababisha underestimations ya ukaaji na wingi katika spishi na tafiti na walikuwa kubwa kwa ajili ya Bay Study. Hata hivyo, mwenendo katika uk occupiance na wingi wa kipindi cha utafiti alionekana kuwa unbiased. Urefu wa samaki na idadi yao kwa ujumla ilihusiana na salinity au conductivity maalum, siku ya mwaka, na joto la maji, lakini asili ya mahusiano ilitofautiana kati ya tafiti na spishi. Pia kulikuwa na utegemezi mkubwa wa nafasi na muda katika ukaaji na wingi wa spishi maalum ambao ulibadilika kwa muda na haukuhusiana na covariates zilizochukuliwa. Matokeo yetu yanaonyesha kwamba wasimamizi kuzingatia kuingiza mbinu kwa ajili ya kukadiria kugundua na kurekebisha data ili kuhakikisha ubora wa data. Kwa kuongezea, mifumo ya nguvu ya nafasi na wakati katika data ya ufuatiliaji inaonyesha kuwa itifaki zilizopo zinaweza kuhitaji kubadilishwa ili kuhakikisha kwamba data na inferences zinaonyesha mabadiliko ya mfumo wote badala ya mabadiliko katika seti maalum ya maeneo yaliyochaguliwa bila mpangilio. Uwezekano wa kuwa na samaki wa asili wa California ni kubwa kwa sababu ya idadi kubwa ya samaki wa asili wa California ambao wameongezeka katika karne ya 20. Kuelewa mlo wa wanyama wa samaki ni muhimu kwa kuelewa athari zao za mtu binafsi, jukumu katika mtandao wa chakula, na athari kwa hatua za uwezekano wa usimamizi. Kwa mfano, katika mwaka wa 2014 na 2015, samaki aina ya Stripped Bass (M. saxatilis), Largemouth Bass (M. micropterus), Channel Catfish (M. punctatus), na White Catfish (M. ameiurus) walichukuliwa sampuli kutoka kwenye maeneo matatu ya maji ya chini ya Mto San Joaquin. Kwa mfano, kila tumbo la samaki (n = 582) lilijaribiwa kwa ajili ya uwepo wa samaki wachanga wa Chinook (Oncorrhynchus tshawytcha) na vitu vingine vya mawindo kwa kutumia mbinu ya barcode ya maumbile. Kwa mfano, samaki aina ya catfish ya Channel ina DNA ya samaki aina ya Chinook katika tumbo lake, na asilimia 27.8 ya samaki aina ya Catfish ya Channel wana DNA ya samaki aina ya Chinook, ikilinganishwa na wanyama wengine watatu wa aina ya catfish. Hata hivyo, spishi za samaki zisizo za asili zilitokea kwa mzunguko mkubwa katika mlo wa spishi zote nne za wawindaji kuliko samaki wa salmoni. Kutumia makadirio ya uchovu kutoka kwa uvuvi wa umeme, tuliweza kuzalisha wiani wa idadi ya watu kwa Bass Striped na Bass Largemouth katika kufikia kwetu. Largemouth Bass iligawanywa kwa usawa katika sehemu zote tatu, kwa wastani wa karibu 333 (± 195 SE) kwa kilomita ya mto. Mimea ya Stripe Bass iligawanywa kwa kiasi kikubwa, kuanzia 21 hadi 1,227 kwa kilomita moja. Kwa kuzingatia idadi ya samaki wa aina ya Salmon, tunachunguza idadi ya samaki wa aina ya Largemouth Salmon, ambayo inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa kuwa inahesabiwa. "Kama ilivyoelezwa katika taarifa ya Jimbo la Sacramento, ""Sacramento River Winter-Run Chinook Salmon"" ni aina ya samaki wa aina ya Chinook, na kwa hivyo, ni hatari kwa jamii ya samaki wa aina ya Chinook, na kwa hivyo, ni hatari kwa jamii ya samaki wa aina ya Chinook." Jitihada moja kama hiyo ni utabiri wa kila mwaka wa idadi ya ndege wachanga wanaotembea wakati wa majira ya baridi kali wanaoingia katika Delta ya Sacramento-San Joaquin. "Uhakiki wa Uzalishaji wa Vijana wa Asili ya Asili (JPE) hufafanuliwa kama ""nambari ya vijana wa majira ya baridi ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi ya majira ya baridi.""" Programu za sasa za ufuatiliaji katika Bonde la Sacramento haziruhusu makadirio ya moja kwa moja ya JPE na kwa hivyo mbinu mbalimbali zimetumika kutabiri thamani hii kila mwaka. Hapa tunaelezea mbinu tatu mbadala kwa ajili ya utabiri wa asili ya asili JPE. Mbinu za hali ya juu (Method 1) ambazo zinaonyesha utabiri wa JEP kama makadirio ya hatua tu, kwa mbinu nyingine mbili ambazo zinaelezea kutokuwa na uhakika wa utabiri kwa viwango tofauti. Kwa kulinganisha utabiri wa JEP kwa mwaka 2018 katika mbinu tatu, njia mbili na tatu zinaongoza kwa utabiri wa chini wa JEP, kwa asilimia 24 na 18 kwa mtiririko huo, hasa kwa sababu ya utabiri wa chini wa mabadiliko ya fry-to-smolt na kiwango cha kuishi cha smolt kinachotokea chini ya Red Bluff Diversion Dam. Kwa sababu makadirio ya baada ya muda wa wingi wa majira ya baridi kali ya vijana kwenye mlango wa Delta haipo kwa sasa, hatuwezi kutathmini ustadi wa utabiri kati ya mbinu tatu. - 1 PDF ya ziada