Observable not assignable to type Observable

I think that your problem is located here:

getRisks(): Observable<RiskListSummary[]> {
  return this.http.get(this.serviceUrl)
     .map(this.extractData()) <== passing result of function
     .catch(this.handleError()); <== passing result of function
}

You could use just passing function reference:

getRisks(): Observable<RiskListSummary[]> {
  return this.http.get(this.serviceUrl)
     .map(this.extractData)
     .catch(this.handleError);
}

but this way you will lose this.

Or you could use bind method to retain this:

getRisks(): Observable<RiskListSummary[]> {
  return this.http.get(this.serviceUrl)
    .map(this.extractData.bind(this))
    .catch(this.handleError.bind(this));
}

however you will lose type checking.

I would leverage arrow functions to be able to use lexical this:

getRisks(): Observable<RiskListSummary[]> {
  return this.http.get(this.serviceUrl)
    .map(res => this.extractData(res))
    .catch(err => this.handleError(err));
}

Without it, the this variable will point to the function where the call is made, instead of the instance that contains getRisks().