DOI: 10.5061/dryad.b8gtht7qn
title: The paradoxical impact of drought on West Nile virus risk: Insights from long-term ecological data

description: Mosquito-borne diseases are deeply embedded within ecological communities,
 with environmental changes – particularly climate change – shaping their
 dynamics. Increasingly intense droughts across the globe have profound
 implications for the transmission of these diseases, as drought conditions
 can alter mosquito breeding habitats, host-seeking behaviors, and
 mosquito-host contact rates. To quantify the effect of drought on disease
 transmission, we use West Nile virus (WNV) as a model system and leverage
 a robust mosquito and virus dataset consisting of over 500,000 trap nights
 collected from 2010-2023, spanning a historic drought period followed by
 atmospheric rivers. We pair this surveillance dataset with a novel
 modeling approach that incorporates monthly changes in bird host community
 competence, along with drought conditions, to estimate the effect of
 drought severity on WNV risk using panel regression models. Our results
 show that while drought decreases mosquito abundances, it paradoxically
 increases WNV infection rates. This counterintuitive pattern likely stems
 from reduced water availability, which concentrates mosquitoes and
 pathogen-amplifying bird hosts around limited water sources, thereby
 increasing disease transmission risk. However, the magnitude of the effect
 depends critically on mosquito species, suggesting species-specific
 behavioral traits are key to understanding the effect of drought on
 mosquito-borne disease risk across real landscapes.
description: # The paradoxical impact of drought on West Nile virus risk: Insights from
 long-term ecological data Dataset DOI:
 [10.5061/dryad.b8gtht7qn](10.5061/dryad.b8gtht7qn) ## Description of the
 data and file structure **Title**: The paradoxical impact of drought on
 West Nile virus risk: insights from long-term ecological data
 **Authors**: S Sambado*, T J Sipin, Z Rennie, A Larsen, J Cunningham, A
 Quandt, D Sousa, and A J MacDonald *corresponding author:
 [sbsambado@ucsb.edu](mailto:sbsambado@ucsb.edu) /
 [ssambado@stanford.edu](mailto:ssambado@stanford.edu) **Description**:
 Observational study using vector control surveillance data paired with
 environmental data to assess the effect of drought on mosquito abundances
 and infection rates in Kern County from 2010-2023. Within-estimator panel
 models (also known as "fixed-effects" in econometrics) found
 that an increase in drought severity led to a decrease in mosquito
 abundances and an increase in West Nile virus infection rates.  **Included
 files:** To re-create figures and analyses from the resulting manuscript,
 users can download the data files (*.csv) and run the scripts
 (wnvdroughtkernfigures_v2.Rmd and wnvdrought_analysis**v2.Rmd).
 **Software:** R version 4.4.1 *package versions: *broom_1.0.5,
 fixest_0.12.1, ggplot2_3.5.2, ggmap_4.0.0, ggpubr_0.6.0,
 modelsummary_2.1.0, RColorBrewer_1.1-3, readr_2.1.5, sandwich_3.1-0,
 tidyverse_2.0.0 ### Files and variables #### File:
 wnvdroughtkern_figures_v2.Rmd **Description:** script to re-create figures
 #### File: wnvdroughtkern_analysis_v2.Rmd **Description:** script to
 re-create data summaries and analyses #### File:
 abund_quin_panel_clean.csv **Description:** *Cx. quinquefasciatus*
 abundance data for panel models ##### Variables * : * clust: assigned
 clusterID to individual trap station * year: year of collection * month:
 month of collection * lat: latitude of clusterID * lon: longitude of
 clusterID * species: species of mosquito (*Cx. tarsalis* or *Cx.
 quinquefasciatus*) * mos_per_trap_night: average mosquito count per trap
 night within a month * pdsi: Palmer Drought Severity Index (e.g., drought
 severity metric) * temp_max_c: maximum temperature (C) * woy_cms_mean:
 average weekly Kern River discharge rate (cms) within a month *
 pdsi_standardized: standardized Palmer Drought Severity Index *
 temp_max_c_standardized: standardized maximum temperature (C) *
 woy_cms_mean_standardized: standardized average weekly Kern River
 discharge rate (cms) within a month * pdsi_standardized_lag_1month:
 standardized Palmer Drought Severity Index from the prior month #### File:
 abund_quinq_full_clean.csv **Description:** *Cx. quinquefasciatus*
 abundance data for figure making ##### Variables * : * clust: assigned
 clusterID to individual trap station * year: year of collection *
 collection_date: date of collection * month: month of collection *
 species: species of mosquito (*Cx. tarsalis* or *Cx. quinquefasciatus*) *
 trap_nights: number of trap nights an individual trap station was deployed
 for surveillance efforts * total_mosquitoes: number of mosquitoes
 collected per trapping effort * mos_per_trap_night: weekly average
 mosquitoes collected per trap night within a month #### File:
 arbonet_ca_clean.csv **Description:** data on reported human WNV disease
 cases in California from CDC ArboNET ##### Variables * : * full_geo_name:
 county identifier * year: year of reported cases * county: county of
 reported cases * activity: type of report (human activity or non-human
 activity) * reported_human_cases: number of reported human West Nile virus
 cases #### File: landuse_clean.csv **Description:** data on land use types
 for trap station clusters ##### Variables * : * lon: longitude of trap
 station * lat: latitude of trap station * land_use2020: full descriptor of
 land use under the trap station * land_bin2020: binned category of land
 use under the trap station #### File: abund_tar_full_clean.csv
 **Description:** *Cx. tarsalis* abundance data for figure making #####
 Variables * : * clust: assigned clusterID to individual trap station *
 year: year of collection * collection_date: date of collection * month:
 month of collection * species: species of mosquito (*Cx. tarsalis* or *Cx.
 quinquefasciatus*) * trap_nights: number of trap nights an individual trap
 station was deployed for surveillance efforts * total_mosquitoes: number
 of mosquitoes collected per trapping effort * mos_per_trap_night: weekly
 average mosquitoes collected per trap night within a month * pdsi: Palmer
 Drought Severity Index (e.g., drought severity metric) #### File:
 trapstation_info_clean.csv **Description:** data on trap station location
 information ##### Variables * : * id: individual trap station ID * clust:
 assigned clusterID for trap station * lat: latitude of clusterID centroid
 * lon: longitude of clusterID centroid #### File:
 pesticide_kernco_clean.csv **Description:** data on pesticide activity in
 Kern County ##### Variables * : * year: year of pesticide application *
 month_in_year: month of pesticide application * pounds_chemical_applied:
 pounds of pesticide applied * mos_life_stage_target: pesticide targeted
 mosquito life stage (larvicide or adulticide) #### File:
 abund_tar_panel_clean.csv **Description:** *Cx. tarsalis* abundance data
 for panel models ##### Variables * : * clust: assigned clusterID to
 individual trap station * year: year of collection * month: month of
 collection * lat: latitude of clusterID * lon: longitude of clusterID *
 species: species of mosquito (*Cx. tarsalis* or *Cx. quinquefasciatus*) *
 mos_per_trap_night: average mosquito count per trap night within a month *
 pdsi: Palmer Drought Severity Index (e.g., drought severity metric) *
 temp_max_c: maximum temperature (C) * woy_cms_mean: average weekly Kern
 River discharge rate (cms) within a month * pdsi_standardized:
 standardized Palmer Drought Severity Index * temp_max_c_standardized:
 standardized maximum temperature (C) * woy_cms_mean_standardized:
 standardized average weekly Kern River discharge rate (cms) within a month
 * pdsi_standardized_lag_1month: standardized Palmer Drought Severity Index
 from the prior month #### File: wnvmir_tar_panel_clean.csv
 **Description:** *Cx. tarsalis* WNV infection data for panel models #####
 Variables * : * clust: assigned clusterID to individual trap station *
 year: year of collection * month: month of collection * lat: latitude of
 clusterID * lon: longitude of clusterID * species: species of mosquito
 (*Cx. tarsalis* or *Cx. quinquefasciatus*) * mir: minimum West Nile virus
 infection rate of the tested mosquito pool * pdsi_standardized:
 standardized Palmer Drought Severity Index * temp_max_c_standardized:
 standardized maximum temperature (C) * woy_cms_mean_standardized:
 standardized average weekly Kern River discharge rate (cms) within a month
 * mean_competence_standardized: standardized average weekly bird community
 competency index within a month * mean_competency: average weekly bird
 community competency index within a month * pdsi_standardized_lag_1month:
 standardized Palmer Drought Severity Index from the prior month #### File:
 wnvmir_quin_panel_clean.csv **Description:**  *Cx. quinquefasciatus* WNV
 infection data for panel models ##### Variables * : clust: assigned
 clusterID to individual trap station * year: year of collection * month:
 month of collection * lat: latitude of clusterID * lon: longitude of
 clusterID * species: species of mosquito (*Cx. tarsalis* or *Cx.
 quinquefasciatus*) * mir: minimum West Nile virus infection rate of the
 tested mosquito pool * pdsi_standardized: standardized Palmer Drought
 Severity Index * temp_max_c_standardized: standardized maximum temperature
 (C) * woy_cms_mean_standardized: standardized average weekly Kern River
 discharge rate (cms) within a month * mean_competence_standardized:
 standardized average weekly bird community competency index within a month
 * mean_competency: average weekly bird community competency index within a
 month * pdsi_standardized_lag_1month: standardized Palmer Drought Severity
 Index from the prior month #### File: climate_full_clean.csv.zip
 **Description:** data on climate summaries in Kern County used for figure
 making. The user will have to unzip the file before using. ##### Variables
 * :  * clust: assigned clusterID to individual trap station * year: year
 of collection * water_year: year of rain season (starts in November, ends
 in March) * tmmx_C: maximum temperature (C) * pr*_sum_wateryear*: sum of
 precipitation (mm) during water year (November through March) ##
 Code/software R version 4.4.1 *package versions* * broom_1.0.5 *
 fixest_0.12.1 * ggplot2_3.5.2 * ggmap_4.0.0 * ggpubr_0.6.0 *
 modelsummary_2.1.0 * RColorBrewer_1.1-3 * readr_2.1.5 * sandwich_3.1-0 *
 tidyverse_2.0.0 ## Access information Other publicly accessible locations
 of the data: *
 [https://github.com/sbsambado/wnv_drought_kern](https://github.com/sbsambado/wnv_drought_kern) Data was derived from the following sources: | **Type** | **Data** | **Source** | \*\*Hyperlink \*\* | | :------------------------- | :--------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | :-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | **Vector** | Mosquito abundance | Kern Mosquito Vectrol Control District (KMVCD) | NA | | Mosquito WNV infection | KMVCD | NA | | | **Host** | Avian host abundance used to calculate bird community competence | eBird (1) | [https://science.ebird.org/en/status-and-trends/download-data](https://science.ebird.org/en/status-and-trends/download-data) | | **Environmental** | Temperature (maximum) | gridMET (2) | [https://www.drought.gov/data-maps-tools/gridded-surface-meteorological-gridmet-dataset](https://www.drought.gov/data-maps-tools/gridded-surface-meteorological-gridmet-dataset)  | | Precipitation (mm) | gridMET (2) | [https://www.drought.gov/data-maps-tools/gridded-surface-meteorological-gridmet-dataset](https://www.drought.gov/data-maps-tools/gridded-surface-meteorological-gridmet-dataset)  | | | PDSI (index -4 to 4) | gridMET (2)  | [https://www.drought.gov/data-maps-tools/us-gridded-palmer-drought-severity-index-pdsi-gridmet](https://www.drought.gov/data-maps-tools/us-gridded-palmer-drought-severity-index-pdsi-gridmet)  | | | Land Cover Type (MCD12Q1)  | MODIS (3) | [https://lpdaac.usgs.gov/products/mcd12q1v061/](https://lpdaac.usgs.gov/products/mcd12q1v061/) | | | Elevation | EarthEnv | [https://www.earthenv.org/topography](https://www.earthenv.org/topography)   | | | River discharge (cms) | USGS NWIS | [https://waterdata.usgs.gov/monitoring-location/11189500/#parameterCode=00065\&period=P7D\&showMedian=false](https://waterdata.usgs.gov/monitoring-location/11189500/#parameterCode=00065\&period=P7D\&showMedian=false)  | | | 30-year normal | PRISM Group, Oregon State University | [https://prism.oregonstate.edu/normals/](https://prism.oregonstate.edu/normals/) | | | Land Cove Type | FFMP | [https://www.conservation.ca.gov/dlrp/fmmp](https://www.conservation.ca.gov/dlrp/fmmp) | | References: (1) Fink et al. 2022, (2) Abatzoglou 2013, (3) Friedl 2022