Climate and Weather Impacts
on West Nile Virus
Nancy Westcott
Midwestern Regional Climate Center, Illinois State Water Survey
Prairie Research Institute, University of Illinois
30th MMCA Annual Meeting
February, 3 2016
Work in conjunction with
◦ Marilyn Ruiz – UIUC, Department of Pathology in
Veterinary Medicine School and Department of
Geography
◦ Juma Muturi – UIUC, Illinois Natural History
Survey, Entomology Laboratory
◦ Surendra Karki – UIUC PHD Student in
Department of Pathology
◦ Rich Lampman – UIUC, INHS, emeritus
◦ Midwest Reg Climate Center staff
◦ NOAA – Micky Glahn, Scott Scallion
Important Climate Parameters
Warmer winter temperatures help
survival of overwintering mosquitos
 Warmer summers help promote growth
of mosquitos and WNV
 Lower summer precipitation amounts
help prevent washout of mosquito
habitats, can prevent dilution of organic
food matter, and often corresponds with
warmer temperatures

Predict WNV Threat Week to Week
Climate – previous WNV summer season
(or months) conditions
 Climate –relationship between preceding
fall, winter and spring seasons (or
months) temperature and precipitation
 Weather – current WNV season weather
from May: daily or week to week.

Prediction Spatial Scale



Dependent on when and where mosquito and
human samples are available for analysis
Moved from County to a Climate Division
scale
And then to a combined Climate Division scale
Michigan Climate Divisions
Historical Wx
Data from
NOAA NCEI:
1895- 2015
High Human
Case WNV year:
2002
2005
2006
2012
MI_SE Winter Max Temperature
2002
2012
2006
MI_SE Winter Min Temperature
2002
2012
2006
MI_SE Summer Max Temperature
2002
2012
2005
MI_SE Summer Min Temperature
2010
2005
2002
MI_SE Spring Precipitation
2012
2005
MI_SE Summer Precipitation
2012
2002
IL NE Summer Precipitation
2005
2012
Michigan

Similar to NE Illinois and elsewhere,
important factors in WNV outbreaks
◦ Warmer winters
◦ Warmer summers
◦ Dryier summers
• So what is our experience with real-time
prediction models based on weather conditions
used in Illinois
West Nile
http://mrcc.isws.illinois.edu/index.jsp
CD NE_IL: 2012: mid-July to mid-August 5 weeks of 350-500 positive
mosquito pools; 2015 very late by comparison.
Fourth Illinois Model
4) Climate Division MIR model
◦ Based on the Cook/DuPage Methodology
◦ Will include forecasts of temperature and
precipitation
◦ Under development
Participants: Surendra Karki
Marilyn O’hara Ruiz
Juma Muturi
Nancy Westcott
Eileen Deremiah (MRCC web master)
Predict Mosquito Infection Rate
By Climate Division by Week
Add 10-dy temperature
And 3-day precipitation forecasts
Four models for four climate regions
Years included for analysis:
2005 to 2013
Data sources
Mosquito test data: IDPH
Weather data: PRISM data from
Oregon State University
All weather variables are
calculated as difference from 30
year normal.
Response variable
MIR Difference from Normal MIR
Results (significan correlations)
Northcentral
Southcentral South
Variables
Prior week's
temperature (Lag1)
North
Winter temperature
Last Summer
temperature
Positive Positive Positive Positive
Last Fall rainfall
Last Winter precip
Positive Positive Positive Positive
Negative Positive Positive
Negative Positive Positive
Negative Negative
Negative
Weekly precipitation and interaction variables were not
consistent in their direction and varied region-wise.
More Results
◦ Lower values of MIR as move from
north to south
◦ Lower correlations of MIR with
weather as move north to south
◦ Why:





less mosquito sampling
fewer humans
different birds
differing bird/mosquito/human interactions
different physical environments for mosquito
habitats
El Nino Greatest
Impact in Winter
Note Wide Spread
of Temperatures,
Above and Below
Average in Summer
After an El Nino
 With
warm winter (so far) and
expected warm summer, under
pressure to get model on line.
 Look for it by the first of June.
MRCC
Weather on Your Birthday Tool
MRCC
Tornado Track Tool